华北南缘南泥湖与北秦岭秋树湾斑岩矿床的对比研究

The Qinling-Dabie molybdenum belt is one of the most important porphyry Mo mineralization zones worldwide, which is host to over 8 million tons of molybdenum, while the East Qinling area hosts the predominant part of the Mo reserve. Most of the Mo ore deposits in the East Qinling area are associated with Mesozoic granites. Even though, the known Mo deposits in the area distribute in both the southern margin of North China Craton (NCC) and North Qinling tectonic units of the East Qinling orogen, however, it is very interesting to note that all of the large Mo ore deposits occur in the southern margin of NCC. Moreover, the few small to middle size Mo deposits in the North Qinling unit are associated with economically significant Cu mineralization which is commonly lack in the southern margin of NCC. The North Qinling block converged with NCC and formed coherent continental block ever since Ordovician and well developed Mesozoic granitic rocks, both as batholiths and stocks. The striking difference in Mo mineralization between the two tectonic units might result from the different basements, sources and magmatic processes of the granite porphyries and different ore forming processes, all of which are far from well documented and well worthy detailed investigation. Systematic comparative study of the two representative Mo deposits from the northern margin of NCC and North Qinling, the Nannihu and Qiushuwan prophyry deposits, respectively, will be the major objective of this study. The sources, temperature, oxygen fugacity, vapor components of the ore-bearing granite porphyries, in-situ analysis of the contents of ore metal as well as halogens (F and Cl) and sulfur in melt- inclusions, and accessory minerals will be investigated to clarify the major controls of the porphyry ore deposits. Meanwhile, the structure and chemical compositions of magmatic and hydrothermal accessory minerals such as apatite, rutile, and magnetite will be analyzed to trace the variations of ore metals during magmatic evolution and the evolving conditions of the hydrothermal fluids. And thus, the geodynamic constraints on the contrasting difference of Mesozoic magmatism and ore forming potential between the North Qinling and Southern margin of NCC are approached. Moreover, indicators of geochemical exploration for porphyry Mo deposits in the region will be established. This study will surely contribute to our understanding of the ore-forming processes and metallogeny of continental subduction-related porphyry Mo deposits in the Mo belt and guide further exploration for Mo mineral deposits in the East Qinling orogen.

东秦岭钼矿带是全球重要的斑岩钼成矿带之一。带内华北南缘和北秦岭两相邻构造单元自早古生代以来即具有统一的演化史，但二者在中生代钼成矿规模和类型方面却有着天壤之别。此差异的起因是一个需要深入探究的科学问题。本项目选取华北南缘南泥湖和北秦岭秋树湾两个斑岩矿床作对比研究。通过含矿岩体Sr-Nd-Pb-Hf-O同位素组成分析其源区组成；借助熔融包裹体微区原位分析，研究岩浆过程对成矿元素和挥发份地球化学行为的控制及其对成矿过程的影响；基于磷灰石、金红石、磁铁矿等矿物结构及组成分析，示踪岩浆演化和成矿过程中成矿金属元素和挥发份F、Cl、S的聚散及其对成矿过程的制约。通过剖析区域基底、含矿岩体源区组成、岩浆温度、氧逸度、成矿金属元素来源和富集成矿机理、成矿多期性等，阐明两构造单元钼成矿差异的主要控制因素，探讨东秦岭巨量钼聚集的机理、建立斑岩钼矿成因模式及找矿模型。

秦岭-大别钼成矿带钼金属储量近千万吨，是全球最大的钼成矿带。>90%的钼矿是与晚中生代花岗岩有关斑岩-矽卡岩型矿床，集中分布于东秦岭至西大别造山带的华北克拉通南缘构造单元。晚中生代爆发性钼成矿以及强烈的不对称分布的控制机理是秦岭-大别造山带深部物质循环、陆造山带成矿学及区域找矿研究的关键科学问题。系统的岩石学、元素及同位地球化学和年代学研究表明，含矿岩体及相关花岗岩类是晚中生代碰撞后伸展背景下滞留在华北南缘深部的扬子俯冲陆壳部分熔融的产物，钼主要来源于扬子上地壳中富钼的沉积岩。含矿斑岩及岩基中的锆石纪录了>10Ma漫长的岩浆汇聚和结晶演化史。花岗岩富钼的源岩及漫长的结晶演化是秦岭-大别钼矿带晚中生代大规模斑岩成矿的两个关键控制因素。与华北南缘不同，秦岭造山带内部燕山期花岗岩具有高Ba-Sr特征，为交代富集岩石圈地幔与下地壳熔体不同比例混合的产物，故成矿以铜为主，钼成矿弱。花岗岩源组成的差异是成矿不均衡性的主导因素。