Structural Characteristics Of The Longshan Dome In Xiangzhong Basin And Its Relation To Low Temperature Ore-forming Elements

The Xiangzhong Basin in the central Hunan province is located on the west side of the Yangtze-Cathysia collisional belt.This area is remarkable for tectonic domes as a result of superposed folds.Associated cryogenic deposits are widely distributed in Xiangzhong Basin,especially within the dome,indicating closely genesis between the tectonic dome and low-temperature mineralization.The Longshan Dome,one of the representative dome in Baimashan-Longshan EW-trending tectonic domal belt,is selected for the objective in this study.Based on the analysis of trace elements,rare earth elements and isotopes,this paper finds out the source of low-temperature ore-forming materials,Pb,Zn,Ag,As and Sb,in Xiangzhong Basin.Through geochemistry and structural analysis of the Longshan Sb-Au deposits,this paper explores the relationship between structural features of domes and low temperature ore-forming materials.The main conclusions are as follows:1.The Longshan Dome is characterized by superposed folds with at least three identified deformations,D1,D2 and D3.D1 are EW-trending fold and axial cleavages;D2 are NWW-NW-trending folds and faults;D3 are NE-SW-trending folds and faults.Using structural analysis,we suggest that Longshan Dome is the result of the NE-trending folds superposed on the EW-trending folds.2.Geochemical results show that:(1)Sb in pre-Devonian is significantly higher than background value,(2)Au in Banxi Group and Lengjiaxi Group is 3 to 10 times higher than background value,and(3)Pb,Zn,Ag and As in Cambrian and Ordovician is higher than background value.The result of rare earth elements and Pb and Sr isotopes suggest that the ore-forming materials,such as Sb and Au,derived from clastics of the basement.3.The Caledonian tectonic event metamorphosed the ore-bearing strata,activated,leached and migrated the ore-forming minerals,.The Indosinian tectonic event forms NWW-NW-trending folds and faults.Late Indosinian magmatism probably arouse the first mineralization of the Longshan Au-Sb deposit.The Yanshanian tectonic event forms NE-SW-trending fold and then superposed on the EW-trending fold.Finally,the Longshan Dome formed as a favorable metallogenic site.This tectonic event simultaneously form NE-tending fault,which is the main ore channel and the ore-bearing structure in this area.Yanshanian magmatism may control the second mineralization of the Longshan Au-Sb deposit.