Field Trips & Events
The Mineral Deposits Division promotes professional development and continuing education of its membership by sponsoring and organizing field trips to mineral districts within Canada and around the world. Published reports prepared by field trip participants ensure that knowledge gained is shared among our large membership. MDD Field Trip destinations are listed below. Follow the hypertext links to MDD Field Trip highlights.
2001 Cordilleran Ore Deposits Field Trip
1998 Abitibi Greenstone Belt
1998 Chibougamu PQ
1998 Gaspe PQ
1995 Southern Africa; The Gangue No. 51
1994 Northeast Russia; The Gangue No. 47
1993 Britannia Mine, BC; The Gangue No. 44
1993 Arizona-Mexico; The Gangue No. 43
1992 Scandinavia; The Gangue No. XX
1992 Southeast BC & northern Washington; The Gangue No. 40
1990 Chile; The Gangue No. XX
1989 Quebec Appalachians; The Gangue No. 28
1983 The Mother Lode District, California
January, 1998 marked the 150th anniversary of the discovery of gold in California. In celebration, a team of geologists at the California Division of Mines and Geology organized a hectic 6-day field trip to a variety of mesothermal, epithermal, hot spring and placer gold deposits across the state. This intensive tour program included 12 mine visits and 6 lectures, along with visits to 2 wineries, the Golden Gate Bridge, San Francisco’s Fisherman’s Wharf and the Las Vegas strip - all achieved against the backdrop of a hurricane.
Highlights included a detailed road tour through geology of the Mother Lode Belt and the western Sierra Nevada, with visits to the Jamestown open pit gold mine (mesothermal), the Lincoln mine underground gold project (mesothermal), Coloma -- site of the January, 1848 gold discovery, the Empire mine for a glimpse of early gold mining history, and Cal Sierra Development’s Yuba gold dredge operation (placer). The tour stopped in at the Ironstone Winery with its display of spectacular gold specimens from Jamestown and other mines
The expedition continued with a road tour through Coast Ranges geology to the dramatic accompaniment of a Level 1 hurricane! Site visits included the hot spring mercury deposit at Sulfur Bank, the Silverado silver mine (epithermal), and Homestake’s McLaughlin open pit gold mine (hot spring). The run to the San Francisco airport allowed time for a stop at Beringer Brothers Winery in the Napa Valley, the Golden Gate Bridge and San Francisco’s Fisherman’s Wharf.
A short evening flight took us to the Southern California Desert for ongoing visits to Mitsubishi Cement Co’s whiting-grade and cement-grade limestone deposits and the U.S. Borax world-class borate deposit (chemical precipitate associated with hot springs and fresh-water lake). These were followed by visits to Molycorp’s unique Mountain Pass REE mine (carbonatite) and the spectacularly exposed Viceroy Gold’s Castle Mountain open pit gold mine (epithermal). The tour wrapped up with a night in Las Vegas at the new Treasure Island Resort on the strip.
Evening Lectures included:
Central Andes Field Trip November 9 -29, 1996
Dr. Al Sangster, Geological Survey of Canada, organized an adventurous three week field trip through the spectacular scenery and the remarkable geology and mineral deposits of southern Bolivia, northern Argentina and northern Chile. In each country, introductory lecture sessions on regional geology and ore deposits complemented the tours.
Geological Highlights included:
BOLIVIA
ARGENTINA
CHILE
Our tour started with two `light days’ to allow recovery from jet lag and adjustment to the high altitude. The program included a city tour of La Paz, the highest capital city in the world, a half-day overview lecture session and an afternoon tour of the nearby Laurani gold property.
Accompanied by a geologist from GEOBOL, the state geological survey, the tour bus set out for visits to the Korri Kollo (Au), Mina San Jose (Sn-Ag) and Mina Bolivar (Sn-Ag-Pb-Zn) mines, followed by a full day tour of Cerro Rico de Potosi. This included surface and underground tours of Mina Cerro Rico (Ag-Sn) and an historical/cultural tour of ancient Potosi village.
Full day geological road tour from Potosi, Bolivia to Humahuaca, Argentina offered spectacular scenery across the altiplano.
We arrived in Jujuy, Argentina for ½ day of lectures organized by Dr. Beatriz Coira, at Universidad Nacional de Jujuy, and covering the geology and metallogeny of northwestern Argentina. A short drive brought us to Salta and an evening barbeque (asado) hosted by Paramount Ventures and Finance.
The next day offered a visit to Cretaceous oolitic carbonate-hosted copper (sedimentary copper) occurrences in the Salta Group, southwest of Salta, along with road stops at key exposures of the regional stratigraphy.
From Salta, we headed westward with geo-stops across the Argentine Puna (altiplano). Then onward through the Andes, passing within the shadow of an active volcano. Near the continental divide between the Atlantic and Pacific watersheds, the 360º panoramic view encompassed 36 volcanic cones! At this point Dr. Guillermo Chong joined our tour, providing many cultural and geological insights along our route into Antofagasta.
At 5000 metres altitude, the visit to the El Laco site marked highest point on the trip. Following our investigation of the El Laco mine magnetite flows, the expedition began the descent from the Andes into, then through the Atacama Desert with visits to a lithium playa quarry, nitrate deposits, geothermal fields and recently active volcanic fields.
The lithium playa deposits of Sociedad Chilena del Litio Ltda. Are situated in Salar de Atacama, the third largest salt lake in the world and home to pink flamingoes and other wading birds. The salar is enriched in borates, potassium and an estimated 40% of world lithium reserves.
Tours of the Chuquicamata (porphyry coppper), Mina Sur (exotic copper) and Mantos Blancos mines followed. A half-day lecture program organised by Dr. Guillermo Chong at the Universidad Catholica del Norte included a visit to the the Geological Museum at Antofagasta.
Setting off southward across the Atacama, we reached Copiapo where the group toured the Refugio, Punta del Cobre, Candelaria, and La Coipa mines in the Maricunga district.
The tour wrapped up with a free day in Santiago and a farewell party at the residencia of hosts Sandy Bishop and James Macdonald.
THE MDD & SEG ON SAFARI
In November 1995, Dick Hutchinson, Pat Sheahan and Dani Alldrick led forty tour participants on a field trip that crossed an entire continent. Over two weeks, the group toured 15 mines, traversed type stratigraphy in different regions, and participated in five lecture sessions as they traveled across the expanse of southern Africa.
An overview of the many highlights during our journey has been prepared by Dick Hutchinson (reproduced from SEG Newsletter, No. 24).
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Forty participants from the Mineral Deposits Division of the Geological Association of Canada and the Society of Economic Geologists returned from this memorable trip marveling at the immensity of South Africa’s great ore deposits, the fascination of their geology, the warmth of our hosts hospitality and the beauty and diversity of this country. We experienced all this as we traveled from the the low veldt in northeastern Transvaal, up the Drakensburg, through the high veldt of western Transvaal and northern Cape, and onward across the Kalahari cover to barren Namaqualand and into the Namib desert at the coast near Oranjemund. Our trvels carried us from urban Johannesburg, through Kimberley, Upington, Pofadder, Springbok and on to magnificent Cape Town.
Des Pretorius, Carl Anhaeusser, Spike McCarthy, Morris Viljoen and Rudy Boer welcomed us at the University of the Witwatersrand with a "warm-‘em-up-braai", and overview talks on South Africa’s gold mining history, and discussions of the regional geology and the deposits to be seen during the following week. Grant Cawthorn then led us north via the Magaliesburg Ridge and out across the flats underlain by the lower layered strata of the Bushveld Igneous Complex to Rustenburg.
The week began with an underground visit to the Merensky and UG-2 platinum "reefs" at Anglo American Platinum’s Rustenburg mine, where we experienced a new use for North American poma lifts - and nobody fell off! We visited the magnificent Union Buildings in Pretoria en route back to Johannesburg. A Tuesday surface traverse with Spike McCarthy took us across the 2,900-2,700 Ma Witwatersrand succession in Johannesburg. This was followed by an underground look at deep mining of the Elsburg conglomerate reefs at JCI Ltd’s Cooke #3 and Western Deeps shafts, and by a fascinating visit to their new open cast operations on the basal Black Reef of the Transvaal Supergroup at Lindums. Morris Viljoen led a Thursday regional surface transect across the Bushveld Igneous Complex, from its granophyric roof rocks through the V-magnetite seams of its Upper Zone in the former Lebowa homeland, and the intricately complex UG-1 seams at Dwars River to Palabora. He accompanied us underground on Friday to see JCI’s stibnite-gold ores in the ca. 2.9 Ga Archean Murchison greenstone belt, and to a final, late stop at a pegmatitic emerald deposit.
The weekend saw us viewing game in Kruger Park - hippos, alligators and giraffe, but apart from a magnificent herd of Cape Buffalo and a few grey humps in the distance that might have been elephants, we didn’t do well on the "big five" (buffalo, elephant, lion, leopard and rhino) due mainly to a rainy afternoon. It was then back to Johannesburg for a flight to Kimberley.
On Monday we toured that historic town, peered into it’s Big Hole, then headed for a look at the Finsch diamond mine and at a kimberlite pipe and kimberlitic dikes that cut stromatolitic dolomites of the Transvaal Supergroup in the nearby Lime Acres limestone quarry. We overnighted at charming Kuruman and were overwhelmed next day by 13 BILLION tonnes of 38% Mn ore in the Kalahari Manganese field. A long drive to Uppington put us in reach Gold Fields’ large, highly metamorphosed, Pb-Zn-Cu-Ag "sedex" deposits at Black Mountain-Aggeneys. We continued to Springbok and its historic old O’Okiep Copper District in northwestern Cape Province. Underground faces of chalcopyrite-bornite ores at Carolusberg and Nigramoep mines, and a surface look at one of the "steep structures" that host the sulphides, left us thoroughly bewildered about the genesis of these truly enigmatic ores (the only other similar example being that at Caraiba in Bahia, Brazil - which incidentally does NOT "fit" to O’Okiep across the `opened’ Atlantic). The final geological highlight was an unforgettable visit to NAMDEB’s alluvial diamond operations north of Oranjemund, Namibia. Here we came to appreciate the stringent security measures (even the writer’s hand lenses were separately X-rayed) after watching vacuum-suction machines inhale diamondiferous gravels from a pre-stripped bedrock surface!
A flight late Friday took us to Cape Town where Faculty of the University of Cape Town hosted the group next morning at Rondebosch. Session included talks by Lawrie Minter and John Gurney. Dr. Minter effectively dispelled the insidious and strangely recurrent CNAH (Creeping North American Hydrothermalist) syndrome that re-infects overseas visitors to the Witwatersrand, and Dr. Gurney convinced us all that from Archean to (and at) the Present, diamonds are forever! Our hosts at UCT sent us off with a delicious, SEG-sponsored luncheon following the morning’s discussions. A cableway trip up Table Mountain was impossible owing to Antarctic winds, but its `tablecloth’ WAS visible; we toured Cape Town’s Waterfront, its downtown and restaurants, sampled the Cape’s wines and sea foods, and circled the Cape Peninsula.
No one explained however, why and how come South Africa should have the world’s largest platinum, chrome, vanadium, gold, manganese, antimony and alluvial diamond deposits, as well as some of its truly unique ones at Palabora and O’Okiep!
Our heartfelt thanks go not only to those named above, but to the many university and mine geologists, their institutions and companies, who so warmly hosted us, so efficiently organized the visits of 40 "foreign invaders", and made our visit to their country so truly memorable.
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Technical notes collected during the South Africa tour follow. Mining districts and deposits are reviewed in geochronological order.
MURCHISON GREENSTONE BELT
Located 450 km northeast of Johannesburg, the Murchison Greenstone Belt (3300 Ma) is an east-northeast trending strip of highly deformed and metamorphosed Archean rocks roughly 140 kilometers long, but less than 15 kilometers wide. The belt is surrounded and locally intruded by Archean granitoids of the Kaapvaal craton. Stratigraphic relationships in the belt remain controversial, reflecting the complex structural and metamorphic history of these rocks. Murchison belt stratigraphy consists of metasedimentary rocks, tholeiitic volcanic rocks, minor komatiitic units and a 3.5 kilometer wide section of felsic metavolcanics.
The belt contains deposits of antimony, gold, mercury, zinc, copper and emeralds. Gold is widespread and occurs in quartz veins hosted by a variety of rocks, in association with iron formations, in arsenopyrite-rich sulphide veins and in antimony-rich quartz-carbonate veins. Small gold deposits are widely scattered throughout the belt and even occur in granitic rocks, but all the major antimony deposits, including the Consolidated Murchison Mine, are situated along the "Antimony Line". Mercury occurs in the same type of deposit as antimony, but on a separate "line" just north of the Antimony Line. Volcanogenic massive sulphide deposits are localized along the Copper-Zinc Line at the contact between felsic metavolcanic and metasedimentary rock packages. Emeralds occur where ultramafic rocks have been altered to biotite schists adjacent to pegmatites and aplites related to granitoid plutons along the southern margin of the belt. Two bands of titanium-rich magnetite and a thin copper-nickel sulphide layer occur within a sequence of meta-diorites to amphibolites.
The Antimony Line is a gently sinuous linear feature 5 to 250 meters wide and 55 kilometers long. . It consists of three horizons of carbonate and talc-rich rocks within a sequence dominated by quartz-sericite and quartz-chlorite schists. There are 18 deposits within the line, however, all mines occur along a 12-kilometer segment of the line. Antimony Line rocks are not common sedimentary or volcanic rocks; trace element and rare-earth element signatures of the talc-carbonate and quartz-carbonate host rocks suggest that most of the rocks of the Antimony Line are altered komatiites. Antimony occurs primarily as stibnite-rich (rarely berthierite) veins in anomalous thickenings of quartz-carbonate rock along the shear. Antimony orebodies are highly irregular, but have tabular shapes and subvertical dips.
The Antimony Line has been interpreted as a late semi-ductile shear zone developed within a broader band of ductile deformation. This structure has subsequently localized alteration and mineralization. Ore deposition was not a single event, but proceeded through successive stages of deformation and metamorphism. The gold-antimony deposits of the Murchison belt have been classed as "carbonated komatiite-related gold deposits" by Viljoen; other examples are the Sheba and Amo deposits of the Barberton Greenstone Belt and the deposits of the Larder Lake Break in the Abitibi Belt.
The Gravelotte Emerald Mine is located on the southern contact of the Murchison Greenstone Belt. The mine has been in production since 1929. Orebodies are irregular and small in size, with average widths of approximately 20 meters. The largest orebodies mined to date are the Cobra, Discovery and Selati deposits. Current mining is in the Cobra North area.
Emeralds crystallized where beryllium-bearing, potassium-rich pegmatites intruded into ultramafic komatiitic schists of the Murchison Greenstone Belt. Emeralds are principally hosted within the biotitic alteration envelope that surrounds the pegmatite; these represent localized zones of intense potassic alteration. A minor amount of emeralds is hosted by the pegmatite.
Emerald production from 1929 to 1986 is estimated at 23,000 kilograms of varying grades. Current reserves are estimated at 17,000 kilograms of emeralds hosted in 1,692,000 tonnes of ore. Emeralds produced at Gravelotte are small, but of good colour and quality. Out of the total production, 30 % of recovered emeralds are saleable, and 2-3 % of these are gem-quality stones. Rough stones sell for $100/carat; top quality cut stones fetch up to $8,000/carat.
WITWATERSRAND SUPERGROUP
The Witwatersrand Basin is asymmetrical, measuring 350 kilometers northeast by 180 kilometers northwest. The succession consists of six kilometers of sedimentary and volcanic rocks. Dates obtained across the Witwatersrand stratigraphy constrain sedimentation to the period 2950-2700 Ma. Once viewed as a long, relatively uneventful period of accumulation of mixed clastic marine sediments, the latest evidence indicates fluvial and lacustrine depositional environments. In addition, the Witwatersrand depositional period is now known to have been accompanied by tectonic activity; spasms of uplift and erosion and major episodes of syn-sedimentary deformation. There was significant deformation at the basin margins, marked by extensional structures and normal faults, however, deformation within the basin was generally minor. The thinning of strata over anticlines is indicative of folding during sedimentation. Synsedimentary faults and monoclines are also recognized as evidence that the craton had split into blocks, with some blocks rising in response to a compressional regime.
Formation of the Vredefort Dome structure at 2020 Ma - almost certainly formed by an impact event - was accompanied by marked downfolding around the perimeter of the dome that is responsible for the preservation of Witwatersrand Basin strata. If it were not for the infolding associated with this impact event, the gold fields of the Witwatersrand Basin would probably have been eroded.
Surface exposure is limited in the areas of the Witwatersrand gold fields, consequently major exploration discoveries have continued from the initial finds of the 1880s to the identification of the Evander gold field in the 1950s. In 1874, Henry Lewis saw rocks near Pretoria identical to those at the Pilgrim’s Rest gold fields far to the east - this drew prospectors into the region for the first time. In 1882 gold was found in quartz veins cross-cutting the lower part of the Witswatersrand sequence. Over the next two years, Fred Steuben was the only prospector working in the area. He found the first gold in conglomerates in 1884. In April 1885 he found gold in conglomerates in the Upper Division - the source of the greatest gold deposits. As Strueben was building a stamp battery, three more prospectors arrived in the area, and the orebody that would become known as the Main Reef Leader was discovered in February 1886 on Farm Langlaagte.
Very rich ore was recovered in the earliest mining operations. 90 tonnes of rock milled in May 1887 averaged 306.59 gm per tonne gold (with gold recoveries estimated to be 60%). The average grade recovered from 22 mines in 1887 was 64.44 ppm. For a strike length of 13 kilometers and within 100 to 150 meters of surface, there was immense secondary enrichment - roughly tenfold - above the grades that are now typically recovered. Modern mining grades are 6 ppm (0.19 troy ounces per ton) gold. Historic gold production now exceeds 1 billion troy ounces, and nearly 20 million ounces are produced annually. The total gold resource of the Witwatersrand basin including past production, known reserves, and subeconomic deposits, is estimated at 80,000 metric tonnes (2 billion ounces).
Only about 10% of Witwatersrand strata consists of conglomerates, and it is only the conglomerates which host the major gold orebodies. Near the middle of the stratigraphic sequence, the 2,880-meter-thick Central Rand Group hosts 95% of the gold resources of the Witwatersrand basin. Production is centered in six districts, Welkom, Klerksdorp, Carletonville, West Rand, East Rand and Evander. Most gold occurs in basal lag conglomerates and trough cross-bedded sandstones. A minor amount of gold is produced from the "carbon leaders", thin algal layers within the sequence. Economic gold-pyrite-conglomerate units are thin sheets, generally less than 20 centimeters thick, but mineralized over vast strike lengths. Throughout the Witwatersrand gold fields, nearly 80 % of gold is associated with pyrite. Quartz pebble conglomerate units contain both primary "buckshot" type pyrite and recrystallized euhedral pyrite. There are also strong correlations between gold, uranium and zircon. The distribution of heavy minerals can be demonstrated to follow patterns predicted by paleobasin morphology and standard hydraulic equations. Periods of uplift during sedimentation led to formation of upgraded placer gold concentrations. Constant reworking in areas of balanced erosion and deposition generated small mineralized areas of greater thickness (tens of meters). Some native gold clearly has the form of rolled abraded nuggets, and some is fracture-related. Some gold grains are flattened with toroidal rims, a form attributed to saltation (aeolian transport), and about 5% of all Witwatersrand quartz pebbles are tumbled or polished wind-faceted ventifacts. A thousand kilometers west of the Witwatersrand, modern-day geologic processes are creating immense volumes of monolithologic quartz pebbles of roughly uniform size. Much of the surface of the present-day Namib Desert is an unconsolidated pavement of rounded, wind-polished quartz pebbles. All finer material has been winnowed away by gusting desert winds. Pebbles of minerals or rocks other than quartz have been eliminated by centuries of sand abrasion. This modern desert surface offers a source area of hundreds of square kilometers of uniformly sized, polished quartz pebbles. Flushed into drainages during flash floods by mass erosion following tectonic uplift, these will accumulate as quartz pebble conglomerate fans on the continental shelf.
The South Deep Mine, now under construction in the Carletonville field, will become the world’s largest gold mine with 60 million ounces of proven reserves. Boasting the world’s tallest headframe (97 meters) and fastest hoists (80 kilometers per hour), the shaft will extend to 2.7 kilometers depth with reserves defined to 3.5 kilometers depth. The $US 1 billion investment decision was based on just ten drill intersections and more than a century of accumulated knowledge about the characteristics and continuity of Witwatersrand gold deposits.
TRANSVAAL SUPERGROUP
The Transvaal Supergroup is an 12,000 meter thick succession of relatively undeformed, unmetamorphosed Early Proterozoic terrestrial and marine sedimentary rocks with minor intercalated volcanics.
These strata host world-class iron, asbestos, manganese, limestone and magnetite orebodies plus diamond-bearing kimberlites and important gold, lead-zinc and fluorite deposits. These rocks also host to the Bushveld Igneous Complex. . The basin-like structure of the Bushveld Complex and the enclosing Transvaal rocks can be appreciated from a spectacular viewpoint - complete with geological model - on Magaliesberg Ridge near Hartebeespoorte dam.
The Transvaal Supergroup consists of two elliptical sub-basins called the Transvaal and Griqualand West subprovinces. These crop out over a large area of northeastern and north central portions of the country respectively. The sequence lies unconformably above the Ventersdorp and Witwatersrand Supergroups and Archean granite-greenstone basement.
Lindum Reefs Gold Mine in the West Rand gold field is hosted in the basal layer of the Black Reef Quartzites, Transvaal Supergroup. The gold deposits have formed only where this regionally distributed unit unconformably overlies steeply dipping gold-bearing strata of the Witwatersrand Supergroup. Gold eroded from the paleoplacer beds of the Elsburg Formation within the Witwatersrand rocks is preserved in the lithified regolith that has accumulated in linear depressions (troughs or paleo-valleys) that were eroded out between more resistent rock layers. Some of these deposits were mined by underground methods in the 1930s; selective open pit mining at Lindum Reefs now recovers grades averaging 3.6 gm per tonne gold, locally reaching 5.4 gm per tonne.
The Lime Acres Limestone Deposit occupies an area about 15 kilometers long and 4 kilometers wide, and holds reserves of high-grade limestone of more than 400 million tonnes - a life of over 100 years at present production rates. The deposit is situated 160 kilometers due west of Kimberley. This area provides all the high grade metallurgical limestone in South Africa. Discovered during the 1950s, the presence of the railway line traversing the deposits was a prime factor in establishing the viability of the limestone. Mining began in 1954.
The limestone is a light to medium grey rock, fine to medium grained in texture and carbonaceous in places. High grade limestone is regarded as that with an analysis of CaCO3 > 95.5, MgCO3 < 2.5%, SiO2 < 1.0%, R2O3 < 1.0%. There appears to be a great deal of biological control of the deposition of the limestone in a shallow and extremely stable marine environment. The presence of stromatolites and algal structures indicate the water was shallow enough to allow sunlight to penetrate to depth, and the continuation of one small stromatolite over 80 kilometers of strike is indicative of the almost undisturbed nature of the basin of deposition.
The Kalahari Manganese Fields, site of the Mamatwan Manganese Mine, are located in the northeastern Cape Province, 60 kilometers northwest of the town of Kuruman. The main field extends between the Mamatwan and Wessels mines and is 35 kilometers long and 5 to 20 kilometers wide. These deposits comprise the largest manganese resource in the world, with an area of 25,000 hectares and reserves estimated at 13 billion tonnes of manganese ore.
This vast deposit was discovered in 1941 at the only outcrop, Black Rock. Initial drill exploration and evaluation was guided by magnetic anomalies as the deposits contain some jacobsite in the lower units. Exploration drilling outlined all the main deposits between 1951 and 1954 and production began in 1954. There are presently two open pit mines and five underground mines in production.
Manganese mineralization occurs within banded iron formation of the Potmasburg Group, Transvaal Supergroup. Strata generally dip gently west at 2-5º. The deposits overlie pillowed basalts and andesites of the Ongeluk Formation. Within the lower 100 meters of the banded iron formation, up to three layers of primary manganese ore occur in thicknesses ranging up to 45 meters. The ores are manganiferous bedded carbonate rocks. Oolitic textures and thin carbonate laminae are common in the lowest band of ore. Primary ores are substantially enriched by near surface supergene processes and by hydrothermal activity near fractures and dykes. A cut-off grade of 37.5% Mn is maintained.
In the Mamatwan open pit, there is only one orebody, reaching up to 45 meters in thickness. The deposit sits within the iron formation about 30 meters above the contact with the lavas. Ore consists of braunite and hausmannite with lesser kutnahorite. Mill capacity is 15 million tonnes a year. The already large ore reserves have potential for down-dip and lateral expansion. However, at present mining rates, reserves are sufficient for 50 years production. Fe:Mn ratios through the district range from 1:8 to 1:4.
The depositional environment for these deposits is interpreted as a "starved basin" lying offshore of an emergent landmass to the north and east. This environment concentrated chemical sediments such as iron and manganese formations followed by overlying limestones and cherts. Protore, a fine-grained carbonate rock containing 27% manganese, was probably precipitated as an oolitic, laminated carbonate sediment in a matrix of gel-like Mn precipitate. Diagenesis produced Mn wad and crystals of cryptomelane, braunite, jacobsite, rhodochrosite and calcite.
BUSHVELD IGNEOUS COMPLEX
The Bushveld Igneous Complex is the world’s largest mafic-ultramafic intrusive body, covering an area of 67,000 square kilometers. The complete section is over 9 kilometers thick. It is compose of a 9,000-meter-thick layered, differentiated cumulate sequence of mafic to ultramafic plutonic rocks (the Rustenburg Layered Suite) and younger granitic hypabyssal and extrusive units (the Lebowa Granite Suite). Rb-Sr ages for the Rustenburg Suite are 2061 ± 27 Ma.
The complex intrudes the 12 kilometer thick sedimentary package of the Transvaal Supergroup, and is roughly oval in outline. In section the rocks dip gently inwards and young towards the center of the complex. In more detail it consists of a series of arcuate lobes termed the far-western, western, eastern and northern lobes which are separated from one another by intrusive granite and younger cover rocks. The mafic rocks of the Rustenburg Layered Suite were emplaced by the repeated intrusions and mixing of two magmas into partly overlapping conical intrusions, corresponding to the western, eastern and northern lobes of the Bushveld Complex. One of the most striking features of the Bushveld Complex is the incredible persistence of even centimeter-thick layers, over many tens of kilometers of strike length. The same steady state conditions which produced such uniform, delicate layering within this huge mass of magma also enabled the concentration of the world’s principal resource of chromium and platinum.
The Rustenburg Suite is divided into five sub-units, from oldest to youngest , the Marginal Zone, the Lower Zone, the Critical Zone, the Main Zone, and the Upper Zone. The Marginal Zone consists of predominantly noritic rocks; thickness varies from zero to one hundred meters. The Lower Zone consists mainly of a layered, repetitive sequence of dunite-harzburgite-pyroxenite. The Critical Zone is subdivided into the Lower Critical Zone, dominated by pyroxenites with minor harzburgites and chromitite layers; and the Upper Critical Zone of layered pyroxenites, norites, anorthosites and chromitites. The Main Zone is the thickest subdivision, comprising over half the intrusion. It is divided into three subzones characterized by abundant mottled anorthosite, homogeneous gabbronorites, and a pyroxenite layer that can be followed for more than 80 kilometers. The Upper Zone consists of layers of anorthosite and cumulus magnetite in mainly ferrogabbroic rocks.
Bushveld deposits, including the Platreef, comprise 75% world PGE resources. PGE-bearing sulphides, in minor quantities, occur in many of the thinly layered rocks within the Rustenburg Layered Suite, but the world’s largest deposits of chromium and platinum occur in the Lower and Upper Critical Zones. There are 13 chromitite layers, including the LG-6 which is worked for chromite. The three horizons of principal economic interest are the Merensky Reef pyroxenite, the platinum-bearing Upper Group 2 (UG-2) chromitite layer and the Lower Group 6 (LG-6 or Steelpoort) chromitite layer. In the western and eastern Bushveld, significant mineralization occurs in six layered units: UG-1, UG-2, UG-3, Pseudoreef, Merensky Reef and Bastard Reef. The Pseudo Reef and UG-3 have limited lateral extent. The total PGE+Au contents for mineralized zones UG-1, UG-2 and UG-3 are 3.43, 9.64 and 4.71 ppm respectively. Total PGE for the Merensky Reef is 8.1 ppm.
The Merensky Reef, ranging from one meter to ten meters thick, is at the base of the larger Merensky Unit within the Upper Critical Zone. The Merensky Reef is a pegmatoidal feldspathic pyroxenite. Chromite occurs throughout the reef, but is concentrated in the upper and lower parts as thin chromite stringers with economic PGE’s, Ni and Cu. The lower chromitite is in sharp contact with underlying white mottled anorthosite; above the upper chromitite is a medium-grained pyroxenite, the Merensky pyroxenite, the lower part of which contains mineralization similar to the Merensky Reef. Pyrrhotite is the most common sulphide, with pentlandite and chalcopyrite. PGE minerals are Pt-Fe alloys, 33%; Pt-Pd sulphides (cooperite and braggite) 29%; Pt-Pd tellurides, 13% laurite, 11%; sperrylite, 11% other PGE minerals, 3%. The PGE contents and proportions in the Merensky Reef vary slightly along strike; in the western lobe, PGE contents range from 11 g/t in the northern area to as low as 8 g/t.
The Upper Group-2 (UG-2) chromitite layer (75 to 250 centimeters thick) lies 50 to 330 meters below the Merensky Reef. It is underlain by a pegmatitic pyroxenite, approximately one meter thick, and overlain by "porphyritic" feldspathic pyroxenite which is petrographically similar to the unit overlying the Merensky Reef and also contains thin chromitite layers at its base. The UG-2 chromitite consists of chromite (60-90%), bronzite (5-25%) and plagioclase (5-15%) with accessory pyroxene and biotite. Sulphides and PGE minerals are different to those in the Merensky Reef, Pd and Ir grades are higher in the UG-2, but sulphides are generally less abundant - consequently UG-2 ores are blended with Merensky reef ores prior to smelting.
Both the Merensky and UG-2 layers are interrupted by circular depressions or "potholes" where ore is absent. Potholes are circular depressions where the reef cuts steeply down across layered units to lower levels in the succession. Potholes range up to hundreds of meters wide and tens of meters deep. The reef thins near the pothole and apart from a thin chromitite stringer, is usually absent where it cuts across the strata. At the lower stratigraphic horizon, the "pothole reef" displays the features of a normal undisturbed reef. It has been suggested that the potholes were formed by current action during convection or during the addition of new magma. Others have suggested that they were formed during a hiatus when hotter, less dense magma, emplaced some distance above the floor of the magma chamber, resulted in superheating of the underlying magma and the resorption of the cumulates on the floor. Disruptions of the reef such as potholes are mined successfully for up to 1-2 meters displacement ("rolling reef"), but areas of more severe "topography" are avoided.
Mining activity in the western and eastern sections of the Bushveld Complex is centered on the Merensky reef and the UG-2 chromitite. At Rustenburg Platinum Mines, 100 kilometers northwest of Johannesburg, seven mines are currently in operation over a 30 kilometer sector of the western lobe of the Complex. The orebodies are accessed by declines or vertical shafts, depending on depth.. One mine is producing from UG-2. Long-term strategy is to complete mining of the Merensky Reef then switch all production to the UG-2. There are at least 25 years of reserves left in the Merensky Reef at Rustenburg Platinum mines, and production from the UG-2 has just begun. The mill processes 25,000 tonnes per day and has an on-site refinery for PGEs and precious and base metals. The mine, mill, smelter and support facilities (including the largest private railway in South Africa) employ 15,000 people.
Merensky Reef in the mine area has an overall PGE tenor of 7-8 ppm, with 5 ppm Pt and relative metal abundances Pt>Pd>Ru>Rh>Au>Ir>Os. 90% of the PGE occur in discrete minerals (PGM); 10% in solution in sulphides. PGE ratios are relatively constant. Gold (0.1 ppm) is found in electrum with an Au:Ag ratio of 2.3:1. Other metal ratios are also consistent: Cu/Ni<1, Pt/Pt>1 (2.8 overall, but 6.1 in the chromitites, a truly remarkable Pt concentration). Similar grades but different ratios apply to the UG-2.
At the nearby Western Platinum Mines, proven reserves are sufficient for >100 years of mining at the current production rate. Some parts along the known strike length of the Merensky Reef have not been mined at all.
Mining of the Platreef, which first began in 1926 and ceased a few years later, recommenced in 1993. The Platreef occurs on the northern lobe of the Bushveld Complex. The lowermost units of the Complex are developed only at the southern end of this northern lobe of the Complex. Northwards, progressively higher units lap onto the floor of the magma chamber; the later magmas appears to have transgressed the lower units. The mineralization of the Platreef extends along the basal contact of the BIC in this area. Therefore, the Platreef zone may be the local equivalent of the Merensky Reef, but it forms the basal portion of the complex in the Potgietersrus area. Mineralization consists of blebs and stringers of sulphides in feldspathic pyroxenite and harzburgite.
The Platreef open pit mine currently produces 200,000 tonnes per month, and will increase progressively to 300,000 tonnes per month by 2006. Drilling during the late 1970s established that the orebody continues down to 700 meters vertical depth; underground mining will be a longer term objective. The orebody is defined by assay cutoff grades, not lithological controls and it varies in thickness from 3 meters to 30 meters. The zone dips 45º east. An average strip ratio of 8:1 is envisaged for the life of the mine. Mining is contracted and concentrate is toll smelted and refined by Rusplats. The average grade is 5.0 gm per tonne PGM, consisting of 49% Pt, 47% Pd and 4% Rh. The Platreef also contains 0.3% Ni, making it an important source for this metal in South Africa. The development of the Platreef by Potgietersrus Platinum heralds a new era of production from "unconventional" platinum resources in the Bushveld complex using low cost, open cast mining techniques.
Transgressive units of coarse-grained ultramafic and mafic pegmatite bodies occur in many areas. These include platiniferous dunite pipes which occur throughout the western and eastern Bushveld Complex. Dunite pipes are surrounded by envelopes of olivine-bronzite-plagioclase. Pipes are perpendicular to the layering in the enclosing bronzitites, and the evidence of chromite in the pipes indicates that chromite layers continue across the pipes. It has been suggested that the pipes formed by reaction of hydrothermal solutions streaming through the layered sequence. Mining has been confined to four pipes, Onverwacht, Mooihoek, Driekop and Maandagshoek, all in the eastern lobe of the Complex. Mining of the pipes ceased in the late 1920s and early 1930s. Production was insignificant in comparison to that from orebodies in the layered rocks. However, some of the highest ore grades in the Bushveld Igneous Complex (up to 30 ppm Pt) have been recorded from the pipes.
PALABORA IGNEOUS COMPLEX
The Palabora Igneous Complex intrudes Archean shield rocks and covers an elongated, kidney-shaped area roughly 6.5 kilometers north-south and 2.5 kilometers east-west. The intrusive complex must have an age greater than 2060 Ma. The complex records an alkaline intrusive cycle which emplaced, in three successive stages, rocks ranging from ultramafic to peralkaline in character. The youngest intrusive phases were a series of variably-textured carbonatite rocks. Copper mineralization was emplaced at the close of the third intrusive stage. Average grade for the deposit is 0.5% copper, but local intrusive phases grade up to 1.0% copper. Principal copper sulphides are chalcopyrite and bornite. Chalcocite and cubanite are rare. Other sulphides are: pyrrhotite, pentlandite, millerite, bravoite, limnaeite, violarite, covellite, tetrahedrite, sphalerite, galena, pyrite and marcasite. Trace amounts of gold, silver and platinum group elements are associated with the sulphide minerals.
The Palabora Copper Mine is one of the largest open cast mines in the world, and the largest in Africa. Production began in 1965 and the mill currently processes 82,000 tonnes per day at an average grade of 0.5% copper, a cut-off grade of 0.1% copper, and an average strip ratio of 0.173:1 . In addition to copper, the deposit produces titaniferous magnetite, baddeleyite, uranium, nickel sulphate and sulphuric acid. These by-products add 25% to the total revenue of the mine. Apatite and vermiculite are also produced from the complex by a separate company, Foskor. Mining at Palabora will evolve to an underground operation about 2002. Combined open pit and underground reserves total 1.2 billion tonnes at 0.59% copper, ensuring that mining will continue far into the next century.
NAMAQUALAND METAMORPHIC COMPLEX
The Aggeneys Mining District lies 120 kilometers east-northeast of the regional center of Springbok. The properties are owned 55% by Gold Fields of South Africa and 45 % by Phelps Dodge.
Mineralization is hosted in the mid-Proterozoic Bushmanland Group of metasediments and metavolcanics (1980 Ma) which is part of the Namaqualand Metamorphic Complex. These rocks have been regionally metamorphosed to amphibolite through granulite facies. The regional stratigraphic sequence, from base to top, consists of augen gneiss, pink gneiss, amphibolite, quartz-biotite-muscovite-sillimanite schist, white quartzite, a 200-meter-thick quartz-feldspar-muscovite-biotite-sillimanite schist which hosts banded iron formation, stratiform barite and base metal sulphide deposits, metaconglomerate, amphibolite and grey gneiss. Manganese-rich garnets are characteristic of this entire sequence. The rocks are highly deformed and record four phases of folding. Sulphide bodies thicken around F2 fold closures, and sulphide lenses are oriented along the plunge of F3 fold axes (30º east-northeast).
Surface showings of copper oxide were first noted in the area in the 1920s. In 1971, Phelps-Dodge geologists recognized major sulphide gossans at Black Mountain and Broken Hill. The stratabound ore deposits of this district are interpreted as metamorphosed Sedex deposits. All the orebodies are associated with a strongly magnetic iron formation. Airborne geophysics has outlined the continuation of this key horizon. Drill-testing of gossans associated with strong aeromagnetic anomalies defined the Black Mountain, Broken Hill, Big Syncline and Gamsberg deposits. Investigation of large areas of desert cover continues, using an exploration strategy of systematic drill-testing of any I.P. anomalies located along the long-established aeromagnetic anomaly trends.
Host rocks at the Broken Hill Mine are schists characterized by chlorite, sillimanite, garnet, anthophyllite, cordierite and feldspar augens. The hangingwall to the upper ore lenses is a relatively pure quartzite with minor garnet and biotite. The mine consists of two superimposed orebodies, each one has a core of massive sulphides with an envelope of banded iron formation. Mineralization has a 1 kilometer east-west strike, and 700 meters of vertical extent (dips vary from vertical to almost flat-lying in deeper parts of the mine). The ore lenses have been traced for 1 kilometer down-plunge (25-30º to the east). Total thickness of sulphide mineralization ranges from 3 to 80 meters, but mineable thicknesses range from 1 to 30 meters. The Upper Orebody is coarse-grained, banded pyrrhotite and contains 20-30% galena and 3-4% sphalerite. Thickness ranges from 1 to 30 meters. This lens has higher Cu, Bi and magnetite contents than the Lower Orebody. The Lower Orebody is fine-grained banded pyrrhotite with 10-12% galena and 3-4% sphalerite. Thickness ranges from 1 to 15 meters. Initial reserves, prior to mining, were 38 million tonnes at 0.45% Cu, 6.35% Pb, 2.87% Zn and 82 gm per tonne Ag. To the end of September, 1994, 18 million tonnes had been mined at a grade of 0.52% Cu, 7.83% Pb 2.93% Zn and 113 gm per tonne Ag. Mining costs are $Cdn 35 per tonne and the production rate is 1.44 million tonnes per year.
Ore at the Black Mountain Mine is more copper-rich, in contrast to the other deposits to the east which are all more zinc-rich. This deposit also consists of two ore zones, a thicker Upper Orebody and a thinner Lower Orebody. A band of leptite, interpreted to be a felsic volcanic layer, separates the two ore lenses. The Upper Orebody is comprised of three types of iron formation: magnetite quartzite, magnetite-amphibolite, and barite-magnetite. Garnet-quartzite forms a halo around the Upper Orebody; it is locally enriched in copper (up to 3% Cu). The Lower Orebody consists of baritic to quartzitic schist with disseminated sulphides. This grades into magnetite-amphibolite. The footwall to the massive sulphide lenses is characterized by abundant sillimanite. Tourmaline occurs in the hostrock quartzites and in the iron formation rocks that are the lateral equivalents to the sulphide lenses. Geological reserves are 81.6 million tonnes at 0.75% Cu, 2.67% Pb, 0.59% Zn and 30 g/tonne Ag. Only 18 million tonnes can be recovered economically. In August 1995 the company started underground work to bulk sample the Lower Orebody.
The O’okiep Copper District extends over 3,000 square kilometers composed of granite-gneiss terrane consisting of Archean to Proterozoic age metasediments and metavolcanics which are intruded by a great variety of plutonic and basic rocks. All orebodies of the district are hosted by intrusions of the Koperberg Suite dated at 1070 ± 20 Ma. Roughly 80 % of these intrusions, termed "basic bodies" or "noritoids", are anorthosites; the remaining 20% range from diorite to norite to enstatite-rich "hypersthenites". Copper grade increases with increasing magmatic differentiation, reflected in the mine geologists’ guide "the higher the biotite content, the higher the grade". The intrusions are emplaced as planar dykes or smaller cylindrical chimneys along the prominent kink folds ("steep structures") which are localized areas of highest strain associated with broader open folds. On a regional scale, outcrops of the noritoids outline a box-work like pattern of prominent east-northeast trending linears and subordinate north-trending linears.
Copper mineralization is restricted to the host intrusive and occurs primarily as disseminations, but inter-connecting veinlets and pods of massive ore also occur. The common sulphide minerals are bornite and chalcopyrite, with lesser amounts of chalcocite, pyrrhotite, pyrite, galena and sphalerite. Magnetite is a common constituent of ore and locally constitutes up to 45% of the rock, consequently magnetic surveys are a primary exploration tool.
Copper occurrences of the O’okiep Mining District were first investigated in this region in 1685. The O’okiep Copper Company formed in 1937 and has since recovered 1.53 million tonnes of copper from 90 million tonnes of ore produced from 30 mines in this district. Individual orebodies range from 0.2 to 34 million tonnes, but most fall between 1 to 5 million tonnes in size. Extremely high grades of 25% copper were encountered within a section of the Okiep mine. The current production rate 160,000 tonnes of ore per month is a combined total from the Carolusberg and Nigramoep mines. Carolusberg is one of the deepest base metal mines in the world, reaching 1.8 kilometers below surface. The total reserve of 55 million tonnes of 1.8% copper is derived from two separate orebodies. Grades increase progressively with depth. Cut-off grades are set at 0.8% copper. The Hoits mine, once a major producer, is being prepared for re-opening.
KIMBERLITE DIAMONDS
The Finsch Diamond Mine is located 160 kilometers northwest of Kimberley. The mine is developed on a kimberlite pipe that is part of the Lime Acres kimberlite cluster, consisting of three pipes and several kimberlite dykes. The Finsch pipe occurs along a northeasterly striking precursor dyke set of hypabyssal kimberlite. At least five phases of kimberlite emplacement resulted in the development of a pipe that tapers from 17.9 hectares in area at surface down to 4 hectares in area at 800 meters depth. The youngest kimberlite phase in Finsch is dated at 119 Ma. Erosion is estimated to have removed 800 to 1500 meters of pipe from the original crater down to the present surface. The uppermost 70 meters of the Finsch pipe was marked by "yellow ground" kimberlite. Finsch is a Group II kimberlite, a phlogopite-rich kimberlite with no ilmenite. Eclogitic nodules are rare in this kimberlite, but peridotite (lherzolitic) nodules are relatively common.
Mining at Finsch was by open pit methods from 1964 until 1990. During this time 78.7 million carats were produced from 97.7 million tons of ore (80.55 carats per hundred tonnes). The minimum cut-off size for recovered stones is set at 1.5 mm. Studies have shown that this eliminates 7% of stones. In 32 years of production, only three stones greater than 150 carats have been recovered. However, they expect 1 stone greater than 100 carats from every 5 million tonnes of ore. Mining is currently by underground open stope methods. The production forecast for 1995 is 2.65 million carats from 3.5 million tonnes of ore (75.71 carats per hundred tonnes). Expected mine life is 30 years.
PLACER DIAMONDS
Diamonds on the Namibian coast were originally discovered at Kolmanskop, near Luderitz, during regular railway maintenance (sand clearing) in 1908. Mining in the central and northern parts of the Sperrgebeit (‘forbidden area’) began in that year and continued until 1935, when the northern mines had been largely depleted. These operations exploited aeolian deposits with average stone sizes of 0.2 carats. In 1926, some men and equipment were moved south to the Orange River, the site of new and spectacular discoveries of alluvial diamonds. Currently producing onshore mines in Namibia are beach and shallow marine deposits at Oranjemund, Auchas and Alexander Bay.
At the mines of Namdeb Diamond Corporation the average thickness of the pay gravels is just 0.8 meters, however the deposit ranges in width from as little as 100 metres up to 3 kilometers wide over the full longshore distance of 300 kilometers. By constructing dykes or berms the company has mined gravels offshore to depths of 14 meters below sea level. Very few unmineralized sections were ever located. It is estimated that less than 2% of the initial diamond resource will have been left behind when the operation commences its shut-down sequence in about 2 years time.
For comparison to metal mining, the "grade" of diamonds to gravel is roughly 3 ppb or 350 million to one. The largest diamond ever recovered in the district weighed 129.76 carats. The processing plant must separate diamonds (3.52 gm/cc) from quartz sand (2.7 gm/cc). Statistical studies of the probability of occurrence versus operating costs dictates that the processing plant must only treat gravel within the size range 2-25 millimeters.
1993 Production Statistics:
Overburden stripped: 30.81 million tonnes Concentrate processed: 13.81 million tonnes
Average Grade: 5.6 carats/100 tonnes (95% gem quality) Carats Produced: 836,244
| Mining Costs | Grade Mined | Tonnes Processed | Avg Stone | Profit | |
| Bucketwheel | US$16/100tn | 0.1ct/100tn | 200,000/mnth | 1 carat | US$4/100 tn |
| Bulldozer | US$56/100tn | 5.6ct/100tn | 300,000/mnth | 1 carat | US$1100/100 |
DeBeers Marine mines offshore marine diamond deposits on the Orange River submarine fan, at depths of 130m, producing over 400,000 carats of gem diamonds annually. These deposits were discovered as the result of a 20 year long prospecting operation, costing in excess of US$100M. Mining employs 4 ships using techniques including drills, seabed crawlers and air lift systems to excavate diamondiferous gravels. Planned expansion of marine production will replace decreasing shore mine production.
Exploration for new deposits continues onshore within the boundaries of the Sperrgebeit by DeBeers-controlled companies and offshore to water depths in excess of 200m by Canadian (Namco), South African (Benguela Concessions, ODM) and Australian (BHP) corporations employing large ships and cutting-edge technologies. Reserves of gem quality diamonds offshore may exceed 100 million carats.
ACKNOWLEDGEMENTS
This remarkable field trip was created by Dick Hutchinson, Pat Sheahan and James Macdonald in special recognition of the 100th anniversary of the Geological Society of South Africa. It also marks the first event co-sponsored by the Society of Economic Geologists and the Mineral Deposits Division of the Geological Association of Canada.
Across South Africa our many hosts granted each and every request for mine visits, and did their utmost to extend their hospitality to our large tour party. The warm reception by geologists, mine staff and management will be long remembered.
Morris Viljoen and Larry Neuhoff of the Economic Geology Division of the Geological Society of South Africa organised a series of lecture sessions throughout the trip. Professor Viljoen also arranged many details of our tour around Johannesburg and the Transvaal. Lawrie Minter at the University of Cape Town contributed a wealth of up-to-the-minute notes from a recently completed field trip to South African mines, and offered guidance on many aspects of the tour.
MDD-SEG South Africa Field Trip -- LECTURE PROGRAM
SUNDAY, NOVEMBER 12: LECTURE SESSION 1
University of the Witwatersrand, Economic Geology Research Unit
Prof C.R. Anhaeusser Archaean Metallogeny of South Africa
Prof D.A. Pretorius Historical Review of Gold in South Africa
Prof T.S. McCarthy Current Thinking on the Witwatersrand Basin
Prof M.J. Viljoen Mineralization in the Bushveld Complex
Dr R.P. Viljoen Aspects of Economic and Exploration Geology in Africa
Prof R.W. Hutchinson Recent Developments in North American Economic Geology
TUESDAY, NOVEMBER 14: LECTURE SESSION 2
Economic Geology Division, Geological Society of South Africa - Johannesburg
Prof H.F. Bonham Jr. Circum Pacific Cu-Au
A.J. Macdonald Eskay Creek Mine - An Exhalative Au-Ag Deposit
D.J. Alldrick Jurassic Metallogeny of the Canadian Cordillera
MONDAY, NOVEMBER 20: LECTURE SESSION 3
Economic Geology Division, GSSA - Kalahari Branch, Kuruman
Prof C.W. Field Hydrothermal Mineral Deposits of the Cascade Range, NW USA
Prof R. Kyle Copper-Gold deposits of the Grasberg-Ertsberg district, Indonesia
WEDNESDAY, NOVEMBER 22: LECTURE SESSION 4
Economic Geology Division, GSSA - Namaqualand Branch, Springbok
H.C. Schultze Kudz Y Kayah VMS Deposit - Geology and Exploration History
G.S. Wells Sedex Deposits of the Gataga District, B.C.
SATURDAY, NOVEMBER 25: LECTURE SESSION 5
University of Cape Town, Dept. of Geological Sciences
Prof W.E.L. Minter Gold Deposits of the Witwatersrand Basin
Prof J.J. Gurney Geology of Diamonds