Ag Polymetallic Deposits Research Articles

Sulfur isotopic composition of the Bainiuchang super-large Ag polymetallic deposit, Yunnan Province, China: Implications for the source of sulfur in ore-forming fluids

The Bainiuchang deposit in Yunnan Province, China, is located geographically between the Gejiu ore field and the Dulong ore field. In addition to >7000 t Ag reserves, the deposit possesses large-scale Pb, Zn, Sn reserves and a mass of dispersed elements (i.e., In, Cd, Ge, Ga, etc.). Based on systematic studies of sulfur isotopic composition, the authors conclude: The Bainiuchang deposit experienced two epochs of metallogenesis, i.e., the Middle-Cambrian sea-floor exhalative sedimentary metallogenic epoch and the Yanshanian magmatic hydrothermal superimposition metallogenic epoch. In the two metallogenic epochs, the δ34S values of sulfides were all near 0, showing a tendency of being enriched slightly in heavy sulfur. The δ34S values of sulfides in the early metallogenic epoch are within the range of 2‰–5‰ with a peak value range of 2‰–3‰ and an average of 3.0‰, and those of sulfides in the late metallogenic epoch are within the range of 2‰–6‰ with a peak value of 3‰–4‰ and an average of 3.9‰. For the single metallogenic epoch, sulfur in the ore-forming fluids in the early epoch already reached isotopic equilibrium and was derived mainly from underneath the magma chamber or basement metamorphic igneous rocks. Sulfur in the sulfides in the late epoch was derived mainly from magmatic hydrothermal fluids formed in the process of remelting of the basement metamorphic igneous rocks.

Geochemical characteristics of volcanic rocks of the Laochang Ag polymetallic deposit, Lancang, Yunnan Province, China

In terms of major element, trace element and REE geochemical characteristics of volcanic rocks in the area studied and by making use of the TiO2-K2O-P2O5, Th-Hf-Ta and Zr-Nb-Y trianglar diagrams and the environmental discrimination diagrams of incompatible element distribution patterns, the authors have drawn some conclusions that are different from those by previous workers. It is concluded that volcanic rocks in the Laochang Ag polymetallic deposit at Lancang, Yunnan belong to continental within-plate alkali basalts, and that their geotectonic setting seems to be at the northeastern margin of East Gondwana Land.

Pb Isotope Study of Some Nonferrous Metallic Deposits in China

AbstractBased on Pb‐Pb isochron data of more than 40 Precambrian polymetallic deposits, the authors consider that there are four mineralization periods for the Precambrian copper deposits in China, and the major copper deposits were formed at about 1800 Ma; there are three mineralization periods for gold deposits formed from Archaean to Proterozoic. By studying hundreds of lead isotope data from some Mesozoic continental subvolcanic Cu and Ag polymetallic deposits and fine‐disseminated gold deposits, the authors found that the calculation based on the lead single‐stage evolution model or two‐stage evolution model cannot give the true ore‐forming ages but can provide more information about mineralization and material sources of the deposits.