MINERALIZACJA POLIMETALICZNA Z KOPALNI BEIYI W OKRĘGU RUD ŻELAZA SHILU NA WYSPIE HAJNAN W POŁUDNIOWYCH CHINACH

Abstract

THE POLYMETALLIC MINERALIZATION FROM THE BEIYI MINE, SHILU IRON ORES DISTRICT, HAINAN ISLAND (SOUTHERN CHINA)Abstract. The famous Shilu iron-polymetallic ore mining district located in western Hainan Island, South China, occurs within Meso- and Neoproterozoic low-grade metamorphosed volcanoclastics and carbonates, that belong to the 6th sequence of the Shilu Group. Granitoid intrusions of different ages occur in the surroundings of the mining area. The Shilu deposit is considered to be a structurally reworked as well as hydrothermally altered and enriched ore deposit of a Banded Iron Formation type. The deposit is a very important iron producer from hematite (and minor magnetite) ores. Our work focused on the polymetallic sulfide mineralization that underlies the iron oxide ores. We selected several samples of sulfide ores from the Shilu deposit of the Beiyi mine and its close vicinity. We performed detailed ore microscopic studies as well as electron microprobe analyses using the CAMECA SX 100 equipped with EDS and WDS systems, Pyrrhotite. chalcopyrite and Co-bearing pvrite (up to 11 wt% Co) dominated among ore sulfides in the studied samples. These ore minerals occur in cale-silicate rocks and strongly silicified diopside. tremolite-bearing rocks, either as disseminated grains, sometimes in veinlets. or in aggregates that may form massive ores. Pyrrhotite and chalcopyrite may contain numerous solid inclusions, overgrowths and intergrowths of subordinate sulfides (sphalerite, galena), sulfosalts (glaucodot, costibite, cobaltite, arsenopyrite, ulhnannite), sulfospinels (siegenite) and cassiterite that belong to the minerals crystallizing at medium to low temperatures. Among these minerals, siegenite and Co-bravoite dominate. Tiny crystals (10-20 µm in size) of Bi-minerals (matildite, cosalite) and argentite are also present. Moreover, in association with barite, calcite and chlorite, Ag-Hg amalgamate and cinnabar can occur. The results of our study point to the multistage medium- to low-temperature hydrothermal precipitation of ore sulfides during 4-5 separate stages. Preliminary results of Re-Os isotope datings indicate that pyrites of younger generation (lack of significant Co admixture) crystallized during 240-260 Ma.