Geology, Geochemistry and Genetic Aspects of Kuroko-type Volcanogenic Massive Sulfide Deposits in Sanjiang Region, Southwestern China

Abstract Yidun Island Arc in Sanjiang Region is one of the important Kuroko-type volcano-genie massive sulfide deposits (VMS) districts in southwestern China. Tectonically, the region is situated in the eastern portion of the Tethys orogenic belt, and is a late Triassic extensional island-arc. The island-arc underwent earlier arc construction, intra-arc rifting, later arc construction and back-arc spreading during its evolution and formed a complete trench-arc-basin system, i.e., the Ganzi-Litang suture zone, forearc basin, outer arc, intra-arc rifting zone, inner arc and back-arc basin from east to west across the island-arc.
Kuroko-type VMS deposits and occurrences discovered so far are limited to within the intra-arc rifting zone of the Yidun Island Arc and tend to occur in groups or clusters distributed in separate fault-bound basins; e.g., Zengke, Gacun and Xiangcheng basins, in which submarine volcanic rocks, especially bimodal volcanic suites, were extensively developed. The VMS deposits formed in the waning stages of volcanic eruption in the late Triassic and are hosted in the uppermost section of acidic volcanic rocks (rhyolitic-dacitic) within a bimodal suite. The orebodies are associated with these host rocks: rhyolitic-dacitic pyroclastic rocks and exhalites and chemical sedimentary rocks.
All VMS deposits in Sanjiang are of the Zn-Pb-Cu type. The architecture of the deposits is twofold, consisting of concordant lenses and layers of massive sulfides and an underlying discordant stockwork. All deposits show metal zoning. The hydrothermal alteration related to mineralization is strong and asymmetrical, and is found dominantly within the stockwork zone and host rocks surrounding the ores. There are two alteration patterns: (1) chloritization — serialization — silicification from outer sides to core of the alteration pipe; and (2) silicification + serialization — silicification + carbonate from ihe lower lo upper part of the alteration pipe.
The mineralization temperatures of ore-forming fluids vary in the range 200°C to 335°C. Thermal evolution of the fluids displays temperature profiles that first increase and Ihen decrease wilh progression of mineralization processes. The majority of black-ore minerals (Groups I and II) formed during intensifying slages of hydrothermal activity, and the majority of semi-yellow-ore minerals (Group III) formed during a thermal maximum. There followed Ihe formation of fine-grained black-ore minerals (Group IV), which interacted with barite layers during deasasing temperature phases.
Oxygen and hydrogen isotope studies show lhat the sources of ore-forming fluids for the Kuroko-type VMS deposits are two-fold: seawater and magmatic hydrothermal solutions, represented by the Kuroko deposils in Japan and Kuroko-type VMS deposils in Sanjiang, respectively. In the latter case the hydrothermal solutions reacted with host rocks and mixed with cold seawater percolating downward, and circulated through volcanic rocks resulting in development of alteration zones and formation of ore minerals in Kuroko-type VMS deposits.
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Summary: Regional and orientation geochemical stream sediment surveys were carried out by the Quebec Department of Energy and Resources in southwestern Quebec, over a part of the Mont-Laurier Terrane of the Grenville Province. The area contains some small stratiform zinc deposits. The response of Zn mineralization to geochemical surveys is weak; the known mineralization is not defined by anomalous samples and consistent patterns. This study uses a technique that increases the geochemical signature of...
Publication: Exploration & Mining Geology
Author(s): CLAUDE BELLEHUMEUR, MICHEL JEBRAK
Issue: 1
Volume: 2
Year: 1993
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Summary: The Corbet deposit is one of 17 proximal Cu-Zn massive sulfide deposits located within the Noranda Cauldron which occurs within the core of the Noranda Volcanic Complex. The deposit is located at the top of the Flavrian Formation, the lowermost formation of the 3000 m thick Mine Sequence; the deposit has yielded 2.75 M tonnes of ore grading 3% Cu, 0.96% Zn, 2.06 g/t Ag and 1.0 g/t Au. The multi-lens Corbet deposit formed within a 250 m wide crater that occurs within a localized breccia pile....
Publication: Exploration & Mining Geology
Author(s): H.L. GIBSON, D.H. WATKINSON
Issue: 1
Volume: 2
Year: 1993
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Summary: Electromagnetic surveys were conducted over the Yava sandstone-hosted lead deposit in Nova Scotia to evaluate the usefulness of such surveys for detecting and mapping sedimentary-hosted metallic ore deposits. Both transient and multifrequency systems were used for that purpose. The deposit consists of three zones of disseminated galena which also contain minor amounts of pyrite and sphalerite filling the interstices of the sandstone grains. Each zone overlies a basement depression and is...
Publication: Exploration & Mining Geology
Author(s): AJIT K. SINHA
Issue: 1
Volume: 2
Year: 1993
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Summary: The process of arriving at the size and grade of: (a) a newly-discovered body of mineralization, (b) a potential ore resource, (c) an orebody proposed for mining, or (d) the ore reserves in a mine, requires fundamental geological, and geometrical determinations as well as physical and chemical analyses. This paper outlines geological and geometrical features considered critical, in the authors' experience, in realistic reserve determination. These are discussed under the headings "The Four...
Publication: Exploration & Mining Geology
Author(s): OWEN OWENS, W.P. ARMSTRONG
Issue: 1
Volume: 2
Year: 1993
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Summary: The Jasper Gold mine in northern Saskatchewan produced a total mill feed of 140 127 tonnes at an average grade of 19.0 g/t Au. Both diamond drilling and chip samples from underground workings returned extremely high values, up to 12 851 g/t (375 oz/T) Au over 0.10 meter from a chip sample. In the presence of such extremely high grades, the accurate estimation of reserves is a major problem.
In the first part of this study, production data from the mine were used to evaluate the results of a...
Publication: Exploration & Mining Geology
Author(s): CHRIS M. HEALEY
Issue: 1
Volume: 2
Year: 1993
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Summary: The East Bull Lake gabbro-anorthosite intrusion is one of several Early Proterozoic layered mafic intrusions occurring along the Southern Province - Superior Province boundary in the Elliot Lake - Sudbury region, Ontario. The base of the East Bull Lake intrusion comprises abundant plagioclase cumulates (Leucogabbronorite Zone) hosting two distinct styles of sulfide mineralization: (1) disseminated magmatic sulfides, and (2) disseminated to massive, structurally controlled sulfides. Both types...
Publication: Exploration & Mining Geology
Author(s): D.C. PECK, R.S. JAMES, P.T. CHUBB
Issue: 1
Volume: 2
Year: 1993
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Summary: The prospective Tulks volcanic belt hosts five significant massive sulfide deposits, Tulks Prospect, Tulks East, Jack's Pond, Daniel's Pond and Victoria Mine, as well as numerous showings and indications throughout its 70 km outcrop length. Regionally, the 498 Ma sequence consists dominantly of felsic pyroclastic rocks and flows with interbedded mafic volcanic units and finegrained sediments, commonly graphitic. Contemporaneous granitoid rocks occur in the south half of the belt. Rocks...
Publication: Exploration & Mining Geology
Author(s): C.B. McKENZIE, D.W. DESNOYERS, D. BARBOUR
Issue: 1
Volume: 2
Year: 1993
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Summary: The Laochang mine, located in the Sanjiang area of southwestern Yunnan Province of China, is a volcanogenic massive Pb-Zn-Cu sulfide deposit. It is hosted by a pyroclastic sequence of Early Carboniferous age, namely the lower member of the Yiliu Group, which was intruded by syenite and rhyolite porphyry. The volcanic suite is basaltic or basaltic-andesitic in composition, has alkaline affinities, and is associated with the initial rifting along the margin of the Baoshan-Shanstate continental...
Publication: Exploration & Mining Geology
Author(s): KAIHUI YANG, XUANXUE MO
Issue: 1
Volume: 2
Year: 1993
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