Zircon U-Pb age, Lu-Hf Isotopic Characteristics and Origin of the Banshanping Granitoid Rocks in East Qinling Orogenic Belt

The Banshanping granitoid rocks distribute in the east of the North Qinling orogenic belt.It is a diorite-quartz diorite-granodiorite-granite series,spreading in a NW-SE direction,and intrudes into the Erlangping Group.The SiO2 content ranges from 57.04% to 76.56%,Na2O from 2.05% to 4.65%,K2O from 0.84% to 3.40%.Major element characteristics indicate that Banshanping granitoid rocks have properties of I type granotoids.SREE ranges from 36.51 ppm to 473.25 ppm,and LREE/ HREE ratios lie between 3.95 and 22.18.Negative Eu anomalies are not obvious in most samples,though there are obvious Nb,P and Ti positive anomalies.The zircon LA-ICP-MS ages of Banshangping granitoid rocks are 496.0±8.1 Ma-486.9±9.3 Ma.Hf isotope shows that 176Hf/177Hf ratios range from 0.282721 to 0.282876,εHf（t） values from 8.5 to 14,all positive,and corresponding modal ages （TDM2） range from 559 Ma to 908 Ma.Based on Hf isotope characteristics and existing SmNd and Rb-Sr isotope data,we consider that the Banshanping granitoid rocks originate from mantlederived material,i.e.the igneous rocks that formed in Neoproterozoic,and there may be a certain amount of crust-derived material during the formation of Banshanping granitoid rocks.

Geological characteristics and the origin of ore-forming materials of(Laozhaiwan gold deposit, Yunnan Province

"Golden triangle"area bordered on Yunnan-Guizhou-Guangxi was one of the most important Carlin-type gold deposits concentration areas.Deep understanding of Carlin-type gold deposits in Guizhou and Guangxi Province had reached through several decades studies,but geological environment was very complex in the southeastern Yunnan,and Carlin-type gold deposits produced in the southeastern Yunnan were different from that of America,few studies were taken there.Based on a large number of field work,studies on the geological characteristics combining with geochemistry characteristics were taken,and analysis the genesis of Laozhaiwan gold deposit.The types of alteration in Laozhaiwan gold deposit were mainly silicification and pyritization,and Gold grade was high when silicification and pyritization were both occurred.It could be caculated that fluid density(g/cm3)varied from 0.7 to 4.9,salinity varied from 0.76%to 0.95%and ore-forming pressure(Pa)varied from 1.81×105 to 49.96×105 according to fluid inclusion test results,showed that Laozhaiwan gold deposit was hypabyssal hydrothermal deposit in low temperature and low salinity.According to composition of fluid inclusion analysis,combining with H-O isotope,made theδD-δ18O figure,showed that the fluid of the deposit rooted in formation water and mixed with meteoric waters later.