山东沂南金场矽卡岩型金铜矿床地质地球化学特征及矿床成因

GEOLOGICAL GEOCHEMICAL CHARACTERISTICS AND GENESIS OF THE JINCHANG SKARN TYPE GOLD COPPER DEPOSIT, YINAN COUNTY, SHANDONG PROVINCE

金场金铜矿床是沂沭断裂带西侧与中生代次火山作用有关金铜矿床的典型代表。该矿地质地球化学特征的综合研究表明：其成矿岩体具有富碱、富钾、富轻稀土和大离子亲石元素的特点，是由成熟度较高的中—下部地壳物质经重熔再生的产物。成矿体系具有高温、弱酸性、偏氧化的介质环境。矿化与斑岩体具密切的内在联系，成矿热液及成矿物质主要来自岩浆体系。

The Jinchang gold copper deposit is a typical deposit related to Mesozoic subvolcanic activities to the west of Yishu deep fault zone The outcropped strata in the mining district are mainly Middle Upper Cambrian series which are lithologically impure limestone, sandstone, shale etc Igneous rocks, including (from early to late )diorite porphyry, biotite granodio rite, amphibole felsite porphyry, felsite porphyry and felsite, are a suite of subvolcanic complexes resulting from differentiation of the same primary magma Among them the felsite porphyry, whose Rb Sr isochron age equals 154 8 ×10 6 a , is closely related to mineralization Orebodies are located mainly in the contact zone between felsite porphyry and limestone Chemically, the ore forming stocks are rich in alkali, potassium, LREE and LILE, with Σ REE, LREE/HREE and δ Eu equal to 79 55×10 -6 , 273 84×10 -6 ,8 79～31 07 and 0 45￣0 87 respectively, which are comparable to corresponding data of the syntectic type granitoids in southeastern China The Sr and Nd isotopic compositions of the felsite porphyry are I Sr =0 7112, ε Nd (t) =14 68～17 64 On the ε Sr (t) - ε Nd (t) diagram, their plots are close to plots of granitic gneisses of Taishan Group It is thus conjectured that the ore forming stocks must have been the syntectic products of middle low crustal materials with higher maturity According to chemical composition investigation of paragenetic garnets and clinopyroxenes in skarns, it is shown that the pH and f O 2 values of the ore forming stage equal 5 89～6 05 and 10 -22 5 ～10 -25 ( t =400￣350℃) Investigations have shown that there exists a close relationship between mineralization and porphyry The δ 18 O H 2O values of ore forming fluids vary from 8 0‰ to 10 8‰,and δ 34 S values of sulfides range from 1 9‰ to 3 5‰ These data suggest that the ore forming fluids were composed mainly of magmatic water, and the ore forming fluids and materials were chiefly derived from the magmatic system