Gejiu Tin Polymetallic Ore-Field: Deposit Model and Discussion for Several Points Concerned

Abstract

Gejiu is the largest polymetallic tin ore-field over the world. It has been known as the Yanshanian ranite-related deposit for long time, but recently some researchers argued that it is a syngenetic deposit formed by marine exhalation or it is a basalt-related. After our field investigation and check the previous data achieved we propose that there are not enough evidences to support the two new concepts. Based on the new data we suggest a mineral model for the olymetallic tin deposits of the Gejiu area. The mineral model is that all the mineralization occurs around the roof pendant of the Cretaceous granites (equigranular granite and porphyritic granite) , i. e. greisen-type, skarn-type, Manto type of cassiterite sulfide, and vein-type quartz-tourmaline mineralization from the contact outside. It also exhibits a zoning of the ore-forming elements, i. e. Sn-Cu-W-Mo, Cu-Sn, Cu, Cu-Pb-Zn concentrated around the Cretaceous granite intrusion. We propose the copper in the ores be mainly derived from the Triassic basalt, whereas Pb-Zn from the Triassic carbonate. Moreover, compared with the Cretaceous metallic mineralization in the other parts of the South China we suggest that large-scale W-Sn mineralization and related magmatic rocks dated to be 80-90 Ma in southeastern Yunnan and western Guangxi are the consequence of lithospheric thinning.