西秦岭温泉钼矿床成矿作用时限及其对斑岩型钼矿床系统分类制约  

Timing and duration of metallogeny of the Wenquan deposit in the West Qinling and its constrain on a proposed classification for porphyry molybdenum deposits

作　　者：邱昆峰[1,2] 李楠[1] Ryan D TAYLOR 宋耀辉[1] 宋开瑞 韩旺珍 张东旭[3] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]美国地质调查局丹佛中心,丹佛80225 [3]甘肃有色地质勘查局天水总队,天水741025

出　　处：《岩石学报》2014年第9期2631-2643,共13页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41030423);公益性行业科研专项经费项目(201411048);中国地质调查局地质调查项目(1212011121090);中国地质大学(北京)基本科研业务费专项资金资助项目(2-9-2014-055)联合资助

摘　　要：斑岩系统是一个涉及岩浆和热液作用的复杂系统,建立精细的斑岩系统成因模型对于寻找更为丰富的金属矿产尤为重要,成矿作用时限是建立成因模型和指导矿产勘查的关键。温泉钼矿床是西秦岭造山带内与晚三叠世花岗岩有关的斑岩型钼矿床,其在西秦岭造山带的独特发育蕴含印支期斑岩成矿作用、大陆地壳演化及矿产勘查关键科学问题。钼矿体主要赋存于温泉复式岩体Ⅱ单元和Ⅲ单元的黑云母二长花岗斑岩和似斑状二长花岗岩中,钼以细脉和浸染状矿化形式产出。赋矿岩石单元锆石U-Pb年龄为224.6±2.5Ma到216.2±1.7Ma,Ⅱ和Ⅲ单元分别侵位于~223Ma和~217Ma,持续约8Myr。辉钼矿Re-Os年龄为212.7±2.6Ma到215.1±2.6Ma,暗示晚三叠世钼成矿作用与花岗质岩浆作用密切时空关系,且成矿年龄稍晚,反映钼矿化主要发生在岩浆作用晚期阶段。成岩、成矿作用发生于华北板块与华南板块全面对接后秦岭造山带构造体制由碰撞到后碰撞的转折阶段,响应南秦岭变质变形、勉-略洋盆闭合及大别-苏鲁超高压岩石板片折返统一地质事件。黑云母K-Ar年龄为207~226Ma,可能反映~223Ma和~208Ma的岩体冷却事件和~216Ma的岩浆-热液成矿作用。锆石U-Pb、辉钼矿Re-Os和黑云母K-Ar多元同位素定年系统准确刻画岩体侵位、热液成矿与冷却事件上有所重叠,岩浆-热液分异演化充分,且具有较高的冷却速率,精确厘定温泉斑岩系统岩浆活动的＂多期性＂（复式岩体）、成矿事件的＂瞬时性＂（~214Ma）和成矿作用的＂持续性＂（~8Myr）。同时,系统对比全球典型斑岩钼（铜）矿床成矿动力学背景,细化分类方案,即产于挤压背景的大洋俯冲和大陆碰撞环境矿床及产于伸展背景的后碰撞、陆缘弧后和板内裂谷环境矿床。明确在大洋俯冲→大陆碰撞→后碰撞→板内裂谷旋回的四个阶段均可以产生规模的斑岩型钼Determining the absolute dhration of magmatic-hydrothermal events leading to the formation of porphyry molybdenum deposits is one of the key questions in economic geology, and it is instrumental to the development of genetic models necessary to explore a category of mineral deposits that provide most of the molybdenum and/or copper to our economy. Studies on the magmatic- hydrothermal evolutionary duration of porphyry molybdenum deposits have important implications for the genesis of such deposits during crustal evolution, and also provide insight into how porphyry deposits evolve, both geochemically and dynamically. The Wenquan Mo deposit, closely associated with the concentrically zoned multiphase Wenquan batholith in the West Qinling orogen, has been well studied with volumes of geochronological data. The composite ore-bearing intrusion ranges in composition from granodiorite to porphyritic monzogranite, and has zircon U-Pb ages ranging from 224. 6 ± 2. 5Ma to 216. 2 ± 1.7Ma, the youngest phase being porphyritic and spatially associated with Mo mineralization. Re-Os dates on molybdenite are between 212. 7 ± 2. 6Ma and 215.1 ± 2. 6Ma, consistent with the age of the ore-bearing phase of the batholith, indicating a close temporal and thus possible genetic relationship between molybdenite mineralization and granitic magmatism, which took place during initial tectonic relaxation following collision of the North and South China blocks. This period also corresponds to metamorphism and deformation in the South Qinling terrane along the suture and the exhumation of the Dabie-Sulu ultrahigh pressure metamorphic rocks to the east. Potassium-argon of biotites have ages ranging from 226Ma to 207Ma, indicating two probable cooling events at ca. 223Ma and 208Ma, and mineralization at ca. 216Ma. Overlapping mineralization ages, based on multiple chronometers, between the intrusive ages and the cooling age suggest a prolonged magmatic-hydrothermal episode responsible for Mo mineralization, and relatively rapid cooling rate

关 键 词：斑岩型钼矿床 成矿作用时限 系统分类 温泉钼矿床 西秦岭 

分 类 号：P618.65[天文地球—矿床学]