Early Cretaceous A-type granites and Mo mineralization,Aershan area,eastern Inner Mongolia,Northeast China: geochemical and isotopic constraints

The Jiazishan porphyry-type molybdenum deposit is located in the eastern Inner Mongolia Autonomous Region in China. Mineralization occurs mainly as veins, lenses, and layers within the host porphyry. To better understand the link between mineralization and host igneous rocks, we studied samples from underground workings and report new SHRIMP II zircon U–Pb and Re–Os molybdenite ages, and geochemical data from both the molybdenites and the porphyry granites. Seven molybdenite samples yield a Re–Os isochron weighted mean age of 135.4 ± 2.1 Ma, whereas the porphyry granite samples yield crystallization ages of 139 ± 1.5 Ma (Jiazishan deposit) and 133 ± 1 Ma (Taolaituo deposit). The U–Pb and Re–Os ages are similar, suggesting that the mineralization is genetically related to Early Cretaceous porphyry emplacement. Re contents of the molybdenite range from 21.74 ppm to 52.08 ppm, with an average of 35.92 ppm, whereas δ³⁴ S values of the sulphide vary from 1.3‰ to 4.2‰. The ores have ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios of 18.178–18.385, 15.503–15.613, and 37.979–38.382, respectively. We also obtained a weighted mean U–Pb zircon age of 294.2 ± 2.1 Ma for the oldest granite in Jiazishan area. All granites are A-type granites. These observations indicate that the molybdenites and the porphyry granites were derived from a mixed source involving young accretionary materials and enriched subcontinental lithospheric mantle. A synthesis of geochronological and geological data reveals that porphyry emplacement and Mo mineralization in the Jiazishan deposit occurred contemporaneously with Early Cretaceous tectonothermal events associated with lithospheric thinning, which was caused by delamination and subsequent upwelling of the asthenosphere associated with intra-continental extension in Northeast China.     

走滑断裂带的两类花岗岩

大型走滑断裂带,由于在水平方向的运动,导致两个区域发生扩张;另两个区域发生压缩。前者控制了拉分火山沉积盆地,形成了与火山作用同源的走滑—拉分张裂型侵入岩;后者控制了菱形地垒,形成了走滑—挤压隆起型花岗岩。这两类花岗岩同时产于同一走滑断裂带的不同部位,因其构造环境不相一致,在宏观上以被动就位和强力就位而有明显区分;在微观上以岩石化学等物质组分或趋近典型的张裂性花岗岩套,或趋近典型的挤压性花岗岩套,而泾渭分明。首次发现的这两类花岗岩并存的实例,为产于辽吉黑东部鸭绿江断裂带中的东宁老黑山—珲春农坪的走滑—拉分张裂型花岗岩套和浑江荒沟山走滑—挤压隆起型花岗岩套。它们形成的时代均属晚三叠世。     

西藏折无地区晚白垩世二云母花岗岩地球化学及构造环境

西藏南木林县折无地区晚白垩世二云母花岗岩K-Ar年龄为93.4 Ma,侵入到石炭系砂岩中.二云母花岗岩中SiO2、Al2O3和K2O质量分数高,A/CNK值大于1.11,并且标准矿物计算的刚玉质量分数均大于2.6%.Rb和Th的富集程度较强,K、Ba、Ta、Nb、Ce均有不同程度的富集,Hf、Zr、Sm、Y、Yb相对亏损.轻稀土相对富集,重稀土亏损,具有明显的负铕异常,属于同碰撞花岗岩类.该区晚白垩世的二云母花岗岩是产生在陆-陆碰撞环境下的过铝质花岗岩.     

彭山矿田锡多金属矿床成矿作用

以地洼成矿理论为基础,从层控、岩控、构控3个方面探讨了江西彭山矿田锡多金属矿床的控矿因素,综述了锡多金属矿床的某些主要特征,指出这些矿床为典型的多因复成矿床。最后,探讨了锡多金属矿床的找矿标志和找矿方向。     

我国显生宙含金花岗岩类岩石-地球化学特征初探

赋存于花岗岩中的金矿床在我国金矿资源中的地位极其重要，并形成我国独具特色的金矿类型。我国含金花岗岩的时代，绝大多数为燕山期，其次是华力西-印支期及加里东期；含金花岗岩体分布广泛，特别集中出露在中朝板块东缘的胶东地体内和北缘广大地区，在北方陆壳增生区及华南扬子板块内亦有分布；研究表明，含金花岗岩类以Ⅰ型花岗岩为主，其次是A型和S型；在同一地区含金花岗岩的金丰度明显高于不含金花岗岩。     

鲍尔羌吉韧变花岗岩类地质特征

产于新疆东准噶尔红柳峡南扎曼苏－鲍尔羌吉变形带蝇的鲍尔羌吉超单元以强烈塑性变形为特征,形成于加里东早期造山运动大陆弧环境,属壳幔混熔的Ｉ型花岗岩。     

新疆库地北中三叠世斑状二长花岗岩锆石U-Pb年龄、地球化学特征及其构造意义

西昆仑山是塔里木地块和羌塘地块在晚中生代碰撞造山的产物,古特提斯洋分支库尔良-阿羌裂谷闭合时限亦存在争议。以库地北斑状二长花岗岩为研究对象,进行岩石学、地球化学和年代学研究。获得LA-ICP-MS锆石U-Pb年龄244.42±0.87Ma,时代为中三叠世。斑状二长花岗岩的SiO_2含量为65.57%～67.70%,Mg~#值为35～38,A/CNK值为0.90～1.01,属于偏铝质高钾钙碱性岩石。稀土元素总量为193×10~(-6)～339×10~(-6),δEu=0.72～0.78,具弱负Eu异常。微量元素Rb、K、Th、U、La、Ce、Zr富集,Nb、Ti、P中等-强亏损。斑状二长花岗岩属于I型花岗岩,源岩为安山岩,形成于俯冲的大陆岛弧环境。结合区域资料和前人研究成果表明,斑状二长花岗岩形成于中三叠世大陆岛弧环境,中三叠世库地一带存在古特提斯洋壳俯冲活动,库尔良-阿羌裂谷尚未消减闭合。     

Petrogenesis,Geodynamics and Radioactivity of the Granitic Rocks of the Nugrus Weakness Zone,South Eastern Desert,Egypt

The studied granitic bodies belong to the south Eastern Desert of Egypt. They extend in a NNW–SSE trend along the same strike of the Nugrus weakness zone by which they are structurally controlled. These rocks are composed of biotite and biotite-muscovite monzogranites to syenogranites. Geochemically, a higher abundance of Ba and Rb in biotite granites with a relatively low abundance in biotite-muscovite granites as well as the diversity of Th, U, Nb, Ta, Zr, and REE reflects their origin from different sources and geodynamic settings. The biotite granites are predominantly metaluminous to low peraluminous whereas the biotite-muscovite granites have a peraluminous nature. Potassium enrichment at the expense of calcium in these rocks reflects a derivation from crustal sources by partial melting in the presence of a volatile system. Radiometric investigation showed high abundances of U(up to 38 ppm) and Th(up to 26 ppm) in biotite-muscovite granites relative to biotite granites(up to 5 ppm U and 18 ppm Th). Radioactive anomalies furthermore have been recorded in parts of biotite-muscovite granites that were affected by the faults(up to 116 ppm eU and 97 ppm eTh). Consequently, biotite-muscovite granites form a potentially fertile source for uranium mineralization.     

川西北平武地区南一里花岗岩体地球化学特征及其构造环境

对出露于碧口地块西南部的南一里岩体进行了系统的地球化学研究,重点讨论了南一里岩体的岩石成因、成岩物质来源及其构造环境.该岩体的SiO2和Al2O3的含量均很高,SiO2含量变化为71.29%～73.05%,A/12NK在1.07～1.11之间;FeO/(FeO+MgO)比值较低,为硅和铝过饱和类型,属典型的强过铝质花岗岩.稀土元素总量(∑REE)为56.80×10-6～89.12×10-6,稀土元素配分曲线呈右倾型,具有弱的负铕异常.Ta、Nb、P、Ti 等高场强元素具有明显的负异常,而Rb和Sr等大离子亲石元素具有明显的正异常.岩浆源区可能是以杂砂岩成分为主的沉积岩部分熔融形成的花岗质岩浆上升侵位形成的,是一种典型的壳源成因类型.南一里岩体具有后碰撞岩浆活动的特征,是印支期华北地块和扬子地块碰撞导致地壳加厚环境下下地壳部分熔融的产物,形成于同碰撞(挤压环境)向碰撞后(伸展环境)转化阶段,为后造山花岗岩类.