Rb-Sr isochron age of sulfides and sulfur isotopic com-position from lamellar ores of the Luotuoshan sulfur polymetallic deposit in western Henan Province and its constraints on the ore genesis

There are considerable debates about the genesis of the Luotuoshan sulfur polymetallic deposit in previous studies. The fo-cus of controversy lies in whether it was formed from the Meso-Neoproterozoic exhalative sedimentary mineralization or not. The lamellar ores are considered as important evidence in sedimentary exhalative mineralization, but the hydrothermal metasomatic genesis is also possible. Therefore, determining the metallogenic epoch and ore-forming material resources of the lamellar ores is the most di-rect and effective way to solve these debates. In the spatial distribution, we found that the lamellar ores mainly occur between skarns and dense massive sulfide ores and some distribute in wall rock such as diopside feldspar and quartz hornfels, skarns and marbles by de-tailed field geological observation. The structure formed by alternate arrangement of different metallic minerals laminas and metallic minerals laminas and wall rock laminas. The geological features suggest that the lamellar ores replace skarns. In this paper, Rb-Sr dating was carried out for nine sulfides samples (comprising six sphalerite and three pyrrhotite samples) from lamellar ores of the Luotuoshan sulfur polymetallic deposit, which yielded an isochron age of 139.6±2.6Ma, suggesting that the metallogenic epoch of Luotuoshan de-posit is Early Cretaceous. Sulfur and strontium isotopes of these sulfides show that δ³⁴S values of the ores have a narrow range of +1.7‰~+3.3‰(averagely +2.44‰), with more obvious tower-shaped distributional features, and that the values of (⁸⁷Sr/⁸⁶Sr)_i range from 0.709704 to 0.709943, with an average of 0.709823, which implies that ore-forming materials mainly originated from deepseated magma of the lower crust. Based on the above analyses in combination with geological investigation in the field and micro-scope observation, the authors hold that the lamellar ores formed in Mesozoic and belonged to magmatic hydrothermal genesis, fur-ther indicating the Luotuoshan sulfur polymetallic deposit is a skarn deposit which belongs to magmatic hydrothermal metasomatic genesis. The results obtained by the authors provide certain theoretical guidance for the future exploration of similar sulfur polymetal-lic deposits in this ore concentration area and even in whole western Henan Province.