Organic Geochemical Evidence and Meachanism of the Genetic Relationship between Organic Matter, Evaporite, and Sandstone-hosted Copper Deposits in Chuxiong Basin, China

Key words: 
• Chuxiong basin /
• sandstone-hosted copper deposits /
• evaporite /
• organic matter organic geochemistry /

Abstract: 

There occur, from down to up, coal-bearing formation (T₃p-T₃g), red cupiferous terrigenous formation (J-K₂d) and red evaporite terrigenous formation (K₂j-K₂z) in the Mesozoic continental Chuxiong basin, Yunnan Province, China. Differences in and relationships of them were stated in the present paper on the basis of studies on assemblage of formations, total organic carbon (TOC), dispersive organic matter soluble organic matter and kerogen. Some conclusions were obtained as follows: (1). the Kangdian continental rift controlled the occurrence of evaporites, copper deposits and coals . Sandstone-hosted copper deposits occurred in the red sandstone which formed when the basin withered, and T OC decreased and salt content increased in the lake water. (2). Organic matter ( OM ) being the type Ⅱ₂ in evaporites had a lower content, and had reached the higher mature stage. However, OM being the type Ⅲ in coal-bearing formation was the richest and had also reached the higher mature stage. OM in copper deposit was the type Ⅲ, but it had even reached the ultimate methane stage. (3). OM and evaporites had played an improtant role in the formation of the copper deposit. OM came mainly from beds and near mudrocks and mobilized and transported copper during the diagenetic mineralization stage. However, during the transformation OM came mainly from coal-bearing formation in the form of reduced copper-and OM-rich deep fluid, while natural water leached evaporites and formed oxidized SO₄^2--rihc saline water. Metallic sulfide formed during the mixing of deep fluid and SO₄^2--rich saline water because OM reduced SO₄^2- into H₂S.