Genesis of the Lala Copper-Cobalt Sulfide Deposit, Sichuan-Province (China) and its comparison with modern marine sulfide occurrences

• Applicant: Professor Dr. Franz Michael Meyer
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2007 to 2009
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 59840390

The Cu-Co bearing Lala massive sulfid deposit is located in south Sichuan (China) not far away from the county center Huili, and is mined in an open-cast working. The lense-shaped ore bodies belong to the middle sequence of young Proterozoic volcano sedimentary rocks, often associated with strongly altered gabbro. Two models are discussed to explain the ore formation: (1) volcano synsedimentary ore formation caused by seafloor hydrothermal circulation; (2) epigenentic hydrothermal ore precipitation caused by metamorphic fluids. In the wider vicinity of the Lala deposit are many more similar layered stratiform ore deposits (often as lenses); only two ore deposits are mined at present. Some of the large ore lenses are aligned in a NW-SE direction. The reason for this remarkable alignment along a strike is unknown. Our research project objective is to solve the genesis of the Lala mineralizations and is based on (1) our own investigations of the mineralogy and geochemistry of rocks and ore samples, (2) the reconstruction of the geological situation at the time of ore deposition and (3) a comparison with data and results from modern seafloor massive sulfide occurrences. The surrounding rocks of the Lala deposit contain two very interesting and distinct altered rock types, these are the quartz-bearing, albitite, which often is the immediate host rock of the ore, and the altered gabbro; the “gabbro” samples also contain sulfide minerals, the mineral augite is mostly replaced by hornblende. It is clear that the formation of these altered types of rocks will play a key role to understand the different steps of the ore genesis. Another part of our geochemical work will consider distinct trace elements which might have survived the metamorphic and deformational geological processes in the rock and ore samples; such data could, for example, indicate the original plate tectonic situation. Our results will also help to classify and to explore more easily the other massive sulfide ore bodies in the Lalachang area.

• DFG Programme: Research Grants
• Participating Person: Professor Dr.-Ing. Peter Halbach