江苏土包山金铁矿床及其成矿机制

THE FEATURE AND ORIGIN OF TUBAOSHAN Au-Fe DEPOSIT JIANGSU PROVINCE

土包山金铁矿床产于石英闪长玢岩火山—侵入体裂隙中的矽卡岩内,与岩浆同化混染和分异作用所形成的贯入型矽卡岩有关,其成岩温度380℃—515℃,磁铁矿成矿温度300℃—380℃,硫化物和自然金的形成温度200℃—310℃,碳、硫、氢、氧同位素资料说明,成矿物质主要来源于地壳深部的岩浆,而成矿溶液主要为岩浆水。

The Tubaoshan Au -Fe deposit,located 2. 5km west to Liyang,is volcanogenic. It occurred at the intersection of E-W trending Nandu -Liyang fault and nearly S -N trending Liyang -Miaxi faults. It is nearly an E -W trending anticline structure, in which D3 -P2strata are cropping in centre and Tertiary cropping in north part,and J3-K1 volcanic series in south part. Many volcanic - plutonic complexes are distributed in the area, widely with alkali alteration. The skarn is developed in quartz diorite with very clear boundary as multiple lens occurred in bed fracture of rock body. The granodiorite destroys the Au - Fe deposit. The deposit composed of two mineralization zones containning three Au ore bodies is formed in skarn. The ores are mainly consisted of metallic minerals - magnetite, pyrite, pyrrhotite arsenopyrite, native gold and nonmetallic mineral -garnet,diopside and calcite,etc. The Au -Fe deposit is formed in second cycle of volcanism with K -Ar isotope age 135. 1 Ma cut by 131. 1 Ma granite - diorite body. The ore forming material come mainly from skarn melt fluids and from strata and volcanic complex rocks. δ13C of skarn shows that it is similar to that of magmatic origin. The data of δ34S of suffide associated with gold show that the S is from deep crust. The δ18O of ore forming fluid is +3^+9. 62‰, and δD = -38. 8~60. 8‰, belonging to magmatic fluid which is varied from high to low with temperature reflected surface water mixing in latter stage of evolution. The data of inclusion determination show that the skarn is formed in 380℃ - 515℃, magnetite in 300℃ - 380 ℃ , and sulfide in 200℃~310℃, with the forming pressure 3× 107Pa^5× 107Pa. The ore forming fluid contains Na+,K+,Mg2+,Ca2+and F-, Cl- , SO42-and Na+>K+,F->Cl-, with varity of high - low - high of salinity. The Au migrates as Na[Au(HS)2], K[Au(HS)2],Na(AuF2) and K(AuCl2) complexes. The elements of vapor phase are H2O CO2CO CH4H2 and N2,in which H2O, CO2 and N2 increase and CO,CH4 and H2 decrease with the ore forming fluid evolution. The rate of CO2/H2O and oxidation coefficient decreases with evolution. The skarn melt formed from magma rising along fracture in volcanism by assimilation and differentiation injected quartz diorite prophyry to form Au -Fe deposit.