MLR key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources

Beijing, China

MLR key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources

Beijing, China

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Qin S.,MLR key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources | Tian G.,China University of Geosciences | Lu L.,China University of Geosciences | Yang S.,MLR key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources
Geological Bulletin of China | Year: 2015

The Century deposit represents an important new member of the major sediments-hosted Zn-Pb-Ag deposits in the Mount Isa inlier and McArthur basin. The deposit is hosted in shales and siltstones of the Mesoproterozoic Lawn Hill Formation. Mineralization comprises fine-grained sphalerite with minor galena and pyrite. Most sulfides (80%-90%) occur as delicate brittle lamellae in black shale units, separated by siderite-rich siltstone horizon. The mineralization shows two large-scale trend, a striking decline in grade from northeast to southwest away from the Termite Range fault, and a more subtle decline in grade from southeast to northwest. Two principal textural varieties of stratabound sphalerite are recognized: "porous, " which has a high pyrobitumen content, and "nonporous, " which has a relatively low pyrobitumen content. The sulfur isotope suggests that the whole fluid system was a large closed system reservoir, with progressive enrichment of heavy sulfur during the deformation and mineralization process. The Century deposit seems to represent an example of shale-hosted mineralization formed during deformation-driven migration of fluids into an over-pressure/under-compacted shale sequence. The influx of relatively hot metal-bearing deep basin brines resulted in the rapid maturation of organic material, which ultimately led to sulfate reduction and base metal precipitation. ©, 2015, Science Press. All right reserved.


Su H.,MLR Key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources | Nie F.,MLR Key Laboratory of Metallogeny and Mineral Assement Institute of Mineral Resources
Geological Bulletin of China | Year: 2015

Abstract: The Fresnillo base metal- silver ore deposit consists of replacement chimney and manto orebodies, disseminated sulfide orebodies, and vein orebodies hosted mainly in Cretaceous marine sedimentary and volcanic rocks. The deposit exhibits southeastward zoned distribution away from a small quartz monzonite stock, and shows increasing silver content and decreasing base metal values with the distance from the stock. Wall rocks adjacent to the stock exhibit silicification and calc-silicate alteration that have been partially replaced by the sulfide minerals. Wall rocks of the vein orebodies exhibit potassic, phyllic, argillic, and propylitic alteration with increasing distance from the orebodies. Homogenization temperatures of quartz, calcite and spharelite in chimney, manto, and deep vein orebodies range from 240℃ to 350℃, while their homogenization temperatures in shallow and distal vein orebodies are between 140℃ and 275℃. Galena δ34S values from all orebodies at Fresnillo vary between -4.1‰ and -8.0‰, while sphalerite δ34S values range between -2.0‰ and -5.0‰. The contrasting δ34S values between galena and sphalerite might have resulted from a slight variation in ore fluid pH (as indicated by the wall rock alteration assemblages) or by increased log fo2. ©, 2015, Science Press. All right reserved.

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