Au-Cu black shale formations in the Asian part of Russia
|Location||International Geological Congress,oslo 2008|
|Holding Date||08 September 2008|
Black shale formations (silty-clayey, clayey--carbonate and siliceous rocks saturated with organic matter) are well known in the Asian part of Russia as concentrators of many metals, including noble, base, rare earth metals and so on. Conditions favorable for the sedimentogenic Au accumulation in black shales are as follows: (i) post-rifting epoch of regional peneplain with the preservation of numerous depressions and scarps to provide seafloor irregularities and hollows during transgression; (ii) the presence of diverse (magmatic, metamorphic, metasomatic, and sedimentary) rocks subjected to hypergenesis; (iii) global transgression coinciding in time with the climatic optimum to provide flourishing biota; (iv) the preservation (up to the maximum moment of transgression) and long-term (dozens of million years) existence of a vast coastal plain and large river systems that collect and transport colloidal and ion solutions of metals; (v) the domination or at least significant share of sapropelic components in the organic matter of sediments.
Copper mineralization in black shales has the following specific features: (i) Cu-bearing formations are confined to orogenic and postorogenic tectonic structures; (ii) the formation of Cu-bearing black shales is favored by a general regression regime with local transgressions producing shallow-water sedimentation basins; (iii) the sedimentation regime is preceded and followed by hot arid climate.