赣南园岭寨大型钼矿岩石地球化学、成岩成矿年代学及其地质意义

江西省安远县园岭寨钼矿是南岭地区新发现的大型独立斑岩型钼矿床,矿体主要产出在园岭寨花岗斑岩与寻乌组变质岩的内外接触带中。通过对园岭寨钼矿系统的岩石学、地球化学和成岩成矿时代研究,结果表明,园岭寨花岗斑岩化学成分具有富K2O(6.52%～8.33%)、P2O5(0.17%～0.21%)、过铝质(A/CNK=1.33～1.59),高Mg#(53～68)、贫CaO(0.37%～2.99%)、Na2O(0.27%～1.01%)和K2O/Na2O>1的特征;微量元素以富含Rb,亏损Ba、Sr等大离子亲石元素(LILE)和富含U、Pb、Nd、Zr、Hf等,亏损Nb、Ta、La、Ce、P、Ti等高场强元素(HFSE)为主要特征,Eu负异常不明显(δEu=0.80～0.90),(La/Yb)N=9.27～13.18,轻重稀土分馏明显。结合成因类型判别图解和矿物学特征,园岭寨斑岩为典型的S型花岗岩,以壳源物质的重熔为主,并受一定程度的幔源物质影响。利用LA-MC-ICP-MS锆石U-Pb年龄,获得了花岗斑岩的成岩年龄为165.49±0.59Ma(MSWD=1.4,n=19);利用辉钼矿Re-Os同位素测年法,获得园岭寨钼矿床辉钼矿的结晶年龄为160±1～162.7±1.1Ma,属赣南燕山期第二次钼成矿作用(150～162Ma)。结合区域年代学资料和已知的矿床(点),指出本区进一步找矿工作应集中在中-晚侏罗世-早白垩世Mo、Pb、Zn等矿床的查找上。

Petro-geochemical Characteristics and Isotope Chronology Study on the Yuanlingzhai Porphyry Mo Deposit in Southern Jiangxi Province

The Yuanlingzhai porphyry Mo deposit,located in southern Jiangxi province,is a newly discovered large-size ore deposit in the Nanling region.The ore body is mainly developed in the contact zone between the Yuanlingzhai granite porphyry and metamorphic rocks of the Xunwu Formation.In this paper,the ages of Mo mineralization and granite porphyry as well as their geochemical characteristics and tectonic environment are studied.The Yuanlingzhai granite porphyry is characterized by high K2O(6.52%~8.33%),P2O5(0.17%~0.21%),Mg#(53~68),peraluminous(A/CNK=1.33~1.59),low CaO(0.37%~2.99%) and Na2O(0.27%~1.01%) contents,and high K2O/Na2O ratio(>1).The rocks are relatively enriched in Rb,U,Pb,Nd,Zr,Hf,but depleted in Ba,Sr,Nb,Ta,La,Ce,P,Ti.Chondrite normalized REE patterns of the rocks show relatively enriched LREE without significant Eu anomalies.Combined with the discrimination diagrams of genetic types and mineralogical characteristics,the granite porphyry is typical S-type granite resulted from partial melting of crustal material with little mantle contribution.The LA-MC-ICP-MS U-Pb dating of zircons from granite yields an age of(165.49±0.59) Ma(MSWD=1.4).Re-Os isotopic dating of molybdenites from the Yuanlinzhai Mo deposit yields age of 160±1~162.7±1.1 Ma,which belongs to the second stage molybdenum mineralization,and it is in accordance with ages of large-scale W-Sn mineralization in Mesozoic in South China.Regarding the isotopic data and discovered deposits,we suggest that the future exploration should be focused on Mo,Pb,Zn deposits developed in Middle-Late Jurassic and Early Cretaceous.