Supergene Mineralization at the Kori Kollo Gold Mine, Bolivia

The Kori Kollo gold deposit is hosted by a c.15 Ma sericitized dacite stock in the La Joya district on the Bolivian Altiplano. The mineralization is of the Bolivian polymetallic vein (BPV) type, with a significant amount of the gold reserves contained in the oxide cap. Field and microscopic studies, K-Ar dating, ??34S values of pyrite, alunite and jarosite, and ??18O values of alunite and jarosite demonstrate that some of this gold is supergene. Two types of supergene gold are present: minute gold grains, 1 to 10 microns across, of high fineness and associated with jarosite and iron oxy-hydroxides; and ‘invisible’ gold, which is probably sorbed onto minerals such as jarosite and iron oxy-hydroxides. Pyrite ??34S values fall in the limited range -3.5 ± 0.6‰, consistent with a magmatic origin. Sulfate ??34S values are homogeneous and overlap closely with those of pyrite (-1.2 ± 2.1‰), which supports petrographic evidence that sulfates replaced pyrite. By contrast, sulfate ??18O values are inhomogeneous with a large range (alunite +2 to 26‰, jarosite -5 to +18‰). These data are interpretedas reflecting kinetically controlled reactions involving various proportions of atmospheric oxygen and local meteoric water. This is typical of supergene alteration and is due to the seasonally dry climate of the Altiplano. The oxide-zone mineralogy is dominated by sulfates and iron oxy hydroxide minerals with some phosphates and halides, which indicates that the groundwaters were acidic, oxidizing and relatively saline. Under these conditions the most likely complexes responsible for gold mobilization are halides. Geological data and K-Ar ages indicate that oxidation of the BPV deposits began at least around11 Ma and possibly up to 15 Ma ago, and that supergene alteration lasted until around 4 Ma. During this period, erosion was minimal. Although supergene processes have been active on the Bolivian Altiplano since the Middle Miocene, in contrast to Northern Chile, enrichment of gold has not occurred.
Keywords: Kori Kollo gold deposit, Mineralization, Bolivian polymetallic vein, Oxide-zone mineralogy
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Summary: The Geological Society has its own quarterly journal called Exploration
and Mining Geology, for the publication of Canadian and international papers on
applied aspects of mineral exploration and exploitation, including mineral
deposit geology, geochemistry, and geophysics, mining geology, mineral resource
appraisal and estimation methods, environmental geology, and case histories. The
editor of the journal is Jeremy P. Richards
Publication: Exploration & Mining Geology
Issue: 3
Volume: 6
Year: 1997
Web Page
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<META content="text/html; charset=unicode" http-equiv=Content-Type>
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<BODY>Gahnite, a zinc-bearing spinel, is a resistate mineral that may be used as
an indicator mineral of polymetallic deposits in high-grade metamorphic terrain.
The Ontario Geological Survey recently completed surficial mapping and sampling
programs in the Separation Lake area of...
Publication: Exploration & Mining Geology
Author(s): T.F. MORRIS, F.W. BREAKS: Ontario Geological Survey, 933 Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 6B5; S.A. AVERILL: Overburden Drilling Management Limited, 107–15 Capella Court, Nepean, Ontario, Canada, K2E 7X1; D.C. CRABTREE
Ontario Geoservices Centre, 933 Ramsey Lake Road, Sudbury, Ontario, Canada, P3E 6B5; A. McDONALD: Department of Earth Sciences, Laurentian University, Sudbury, Ontario, Canada, P3E 2C6
Keywords: Gahnite, Resistate mineral, Polymetallic deposits, metamorphic terrain, Mineralization
Issue: 3
Volume: 6
Year: 1997
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Summary: Rare earth element (REE) data are reported for ores, sulfide-bearing rocks and host rocks from massive sulfide deposits and barren sulfide facies iron formations in Proterozoic volcanic rocks of the Flin Flon-Snow Lake area, Manitoba. Some of the rare earth elements (e.g., Eu), are selectively leached in zones of intense alteration and redeposited together with the sulfides and silicates in the uppermost parts of the alteration zones and at the rock-water interface. Chondrite normalized REE...
Publication: Exploration & Mining Geology
Author(s): G.H. GALE: Department of Energy and Mines, Geological Services Branch, 1395 Ellice Avenue, Suite 360, Winnipeg, Manitoba, Canada R3G 3P2; L.B. DABEK: Department of Geology, University of Regina, Regina, Saskatchewan, Canada; M.A.F. FEDIKOW: Department of Energy and Mines, Geological Services Branch, 1395 Ellice Avenue, Suite 360, Winnipeg, Manitoba, Canada R3G 3P2
Keywords: Rare earth element, REE, Ores, Massive sulfide deposits, Iron formation, Manitoba, Exploration, Ore equivalent strata
Issue: 3
Volume: 6
Year: 1997
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Summary: Gamma-ray spectrometry, an effective tool in geological mapping, was used to define boundaries between various lithological formations in three adjacent areas of Central Syria, namely, the Syrian Desert, Ar Rassafeh Badiayat and the Northern Palmyrides mountains. This paper describes the role of an airborne gamma spectrometric survey which was orginally undertaken to assist uranium exploration. Interpretation of the total count data obtained through the survey has led to significant modificat...
Publication: Exploration & Mining Geology
Author(s): Y.M. JUBELI: Department of Geology and Nuclear Ores, Atomic Energy Commission
P.O. Box 6091, Damascus, Syria
Keywords: Gamma-ray spectrometry, Geological mapping, Syria, Uranium exploration
Issue: 3
Volume: 6
Year: 1997
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Summary: <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD>
<META content="text/html; charset=unicode" http-equiv=Content-Type>
<META name=GENERATOR content="MSHTML 9.00.8112.16440"></HEAD>
<BODY>To evaluate geochemical aspects of sheared zones, 35 samples of granitoid
rocks from an area of shearing &gt;5 km2 at Derehamzeh, Iran were studied
geochemically. Relatively unaltered samples within the shear-zone area average
38 ppm Cu, 1.45 ppm Mo, 4.6 ppb Au, 0.21 ppm Ag, &lt;1...
Publication: Exploration & Mining Geology
Author(s): A. AFTABI: Department of Geology, Shahid Bahonar University of Kerman, Kerman, Iran
Keywords: Geochemistry, Granitoid rocks, Hydrothermally-altered samples, Porphyry copper mineralization
Issue: 3
Volume: 6
Year: 1997
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