The Characteristics And Genesis Of Kaerqueka Copper Polymetallic Deposit, Qinghai Province

Kaerqueka copper polymetallic deposit is located in the southwestern margin of the Qaidam Basin, which is one of medium size deposits recently discovered in Qimantage area, east Kunlun. The host rocks of Kaerqueka copper polymetallic deposit are Early Indosinian Periods intermediate-acid intrusive rocks as well as Ordovician to Silurian Tanjianshan Group marble and basic volcanic rocks. Mainly magmatic rocks of Kaerqueka are porphyroid biotite admellite and granodiorite, and the latter is closely related to mineralization. Mainly magmatic rocks are proved to be calc-alkaline series and I-type granite after the analysis of geo-chemistry. Northwest of Kaerqueka (A area) have the characteristics of porphyry-type mineralization as well as mid-eastern of Kaerqueka (B and C areas) are skarn-type and hydrothermal vein type mineralization.The study shows that fluid inclusions in skarn-type ore typically are aqueous FI (type I) while those in porphyry-type mineralization granodiorite mostly are aqueous FI (type I) and daughter mineral-bearing FI (type II) as well. The homogenization temperatures of the fluid inclusions in the skarn-type ore and in the porphyry-type mineralization granodiorite separately vary from170to260℃and290℃to380℃. The salinities of type I fluids inclusions in skarn-type ore range from0.7%to12.7%(NaClequiv.); and5.9%to22.9%(NaClequiv.) in porphyry-type mineralization granodiorite, while type II fluids inclusions in porphyry-type mineralization granodiorite range from30.8%to59.1%(NaClequiv.). Analytical results of colony composition for fluid inclusions show that liquid components of fluid inclusions are mainly Cl-, NO3-, SO42-, Na+, K+and Ca2+, and gas components are mainly H2O, with minor CO2, H2, CH4, C2H2and C2H6. The study demonstrates that fluid-boiling occurred in porphyry-type mineralization stages, and the ore-forming temperature is from290℃to320℃, the ore-forming temperature of skarn-type stage increased5-6℃after correcting. The capture pressure was calculated between70bar to108bar. It is deduced the depth of mineralization was from0.7km to1.1km based on the pressure.Metallogenic materials of Kaerqueka deposit are mainly from the mantle derived magma which mixed with crustal rocks, and ore-forming fluid is from the magmatic fluid which rich in Na+and metallogenic materials.The ore-forming fluid is characterized by high-temperature (500℃), hypersaline (60wt%). That intermediate-acid magmas riched in metallogenic materials intruded upward during Late Triassic formed porphyry-type mineralization in altered fracture zone of porphyroid biotite admellite. Alterations such as skarnization, greisenization, sericitization, silicification formed at the contact zone of rock body and wall rock, precipitation and enrichment of metallogenic material because of metasomatism and the change of physicochemical conditions, then skarn-type mineralization (B area) and hydrothermal vein type mineralization (C area) were formed.