福建上杭单竹坪矿床早白垩世岩浆作用及地质意义

单竹坪矿床位于福建省上杭县紫金山矿田的西南部, 形成了Au、Cu和Mo异常, 其中Au、Cu富集成矿。选取单竹坪矿床钻孔岩芯中二长花岗岩和花岗闪长岩作为研究对象, 开展岩石学、岩相学、全岩地球化学、锆石U-Pb年代学和Lu-Hf同位素研究。研究结果表明, 二长花岗岩和花岗闪长岩锆石²⁰⁶Pb/ ²³⁸U加权平均年龄分别为105.2Ma和113.4Ma。二长花岗岩和花岗闪长岩具有富钠(Na₂O/K₂O>1), 过铝质(A/CNK=1.19~1.68), 富集轻稀土(LREE)、大离子亲石元素(LIEE, 如Ba、K)和Th、U、Pb和Hf等元素, 亏损高场强元素(如Nb、Ta和Ti等)的特征, 属于高钾钙碱性过铝质岩石系列, 具有岛弧岩浆岩特征。同时具有中等的(La/Yb)_N值(13.6~17.4), 高Mg^#值(45.89~48.53), 以及Eu弱负异常(δEu=0.79~0.97)和Ce弱正异常(δCe=1.0~1.08)。锆石两阶段Hf模式年龄(t_DM2)峰值分别处于0.95~1.0Ma和1.05~1.10Ma区间; ε_Hf(t)值分别介于-4.47~+2.38和-2.73~+1.47, 二长花岗岩以负值为主, 花岗闪长岩正负值均有。综合研究认为, 二长花岗岩来源于中元古界未受幔源组分影响的古老基底地壳熔融而成, 花岗闪长岩来源于新元古界地壳物质并经历了壳-幔混合作用; 单竹坪矿床形成于燕山晚期岛弧或活动大陆边缘构造环境, 与古太平洋板块的俯冲相关, 其西南部或南部是成矿远景区。

The Early Cretaceous magmatism and geological implication of Shanzhuping deposit in Shanghang region,Zijinshan ore field,Fujian Province,Southeast China

Shanzhuping deposit is located in the southwestern Zijinshan ore field, Shanghang County, Fujian Province, develops the Au, Cu and Mo elements anomaly, and forms Au and Cu deposit. The granodiorite and monzogranite are selected for carrying on petrology, petrography, whole rock geochemistry, U-Pb geochronology and Lu-Hf isotope. Here we report the monzogranite and granodiorite 206Pb/238U weighted mean age at 105.2Ma and 113.4Ma. Combined with the zircon characteristics of magma oscillation and Th/U ratios, which reveals that there are two episodes magmatic activities of Late Yanshanian. The granodiorite and monzogranite share geochemical affinities with typical island arc, enriched Na element (Na2O/K2O > 1), light rare earth element (LREE), large icon lithophile element (LIEE, such as Ba and K), and U, Th and Pb etc., depleted high field strength element (HFSE, such as Nb, Ta and Zr), and characterized with peraluminous (A/CNK with 1.19~1.68), medium (La/Yb)N (13.6~17.4), and high Mg# (45.89~48.53); slightly negative Eu anomaly (δEu ranges 0.79 to 0.97), and slightly positive Ce anomaly (ranges 1.0~1.08). The peak value of zircon two-stage Hf model age (tDM2) ranges of 1.05~1.10Ga and 0.95~1.0Ga, the εHf(t) ranges of -4.47~+2.38 (mainly negative values) and -2.73~+1.47 (mainly positive values), respectively. Based on previous research results and opinions of this study, we infer that monzogranite derived from melting of Mesoproterozoic ancient basement in upper crust, while granodiorite derived from the Neoproterozoic crustal material and subjected to the contamination of mantle materials. The Shanzhuping deposit formed in Late Yanshanian island arc or active continent margin tectonic setting, which is closely related to paleo-Pacific plate subducted to Eurasian plate, and the southwest or south of which was predicted as two favorable exploration region.