【作者】 田黎萍；

【导师】 汤中立；

【作者基本信息】 兰州大学 ， 地质工程， 2010， 博士

【摘要】 化石沟铜矿区位于阿尔金与南祁连构造带的交汇部位,晚古生代花岗质岩浆作用强烈,伴有Cu-Au矿及W-Sn矿化。长期以来,研究区内花岗岩类的成因及成矿作用一直未能开展系统深入的研究,导致找矿勘探难以取得突破的进展。本文在国内外花岗岩与成矿作用最新研究成果的基础上,以板块构造理论为学术指导,利用岩石地球化学、同位素地球化学及大地构造学等多学科的综合研究方法,采用现代测试技术为手段,以研究区内花岗岩成岩成矿的动力学过程及模式为研究目标,取得了新的认识和进展。1)通过野外地质调查,结合前人的研究成果,认为化石沟矿区应属南祁连构造带西端南缘,紧邻中阿尔金和北阿尔金构造带,其构造-岩浆-成矿作用受到阿尔金构造系统和南祁连构造系统演化过程的共同控制;2)在花岗岩矿物学、岩石学研究基础上,通过岩石地球化学重新对区内花岗岩类型进行划分,划分出花岗闪长岩(Ⅰ-型)、石英闪长岩(Ⅰ-型)、英云闪长(斑)岩(Ⅰ-型和S-型)、二长花岗岩(Ⅰ-型和S-型)以及蚀变岩(绢英岩)；3)首次在研究区内开展高精度的花岗岩锆石LA-ICP-MS U-Pb同位素年代学研究,获得分布在F1断裂带西侧的花岗闪长岩(YQ-57)锆石LA-ICP-MS U-Pb加权平均年龄为368.7±3.5Ma;分布在F1、F3断裂带之间的花岗闪长岩(YQ-1)年龄为261.1±3.8Ma、二长花岗岩(YQ-25)年龄为252.0±2.1Ma、石英闪长岩(YQ-81)年龄为261.8±1.5Ma、英云闪长斑岩(YQ-89)年龄为262.2±1.4Ma,上述年龄均代表岩石结晶的时间。同时指出,在晚古生代研究区发生过两次重要的伸展构造-岩浆事件,分别为369Ma和262-252Ma,为构建区域地质事件提供了重要的年代学依据；4)通过花岗岩主量元素、微量元素、稀土元素及Sr-Nd-Hf-O同位素地球化学综合研究表明：(1)晚泥盆世花岗闪长岩(368.7±3.5Ma)为高钾钙碱性系列,低Sr高Y(Yb),明显富集Rb、K、Th、Zr-Hf以及LREE,相对亏损Ba、Nb、Ta、Sr、P、Ti,δEu=0.64-0.89；极高的(87Sr/86Sr)I(0.712261-0.712614)和低的(143Nd/144Nd)I(0.511838-0.511825),负εNd(t)值(-6.74804—-6.98879)和(176Hf/177Hf)I=0.282487,εHf(t)=-2.3339,反映源岩为高度富集的地壳物质,岩浆分异程度较低,源区主要残留相为斜长石+角闪石+辉石；(2)中二叠世花岗闪长岩(261.1±3.8Ma)具富钠贫钾,为钙碱性Ⅰ型花岗闪长岩；具高Sr低Y,富集Rb、Th、U、K、Sr、Zr-Hf及LREE,相对亏损Ba、Nb、Ta、P、Ti,δEu平均为0.83;(87Sr/86Sr)I为0.706963-0.706571,(143Nd/144Nd)I为0.512246-0.512266,εNd(t)=-1.23847和-0.84907, (176Hf/177Hf)I=0.282766,以及高的δ18Ov-SMOW值(12.1-12.5%o),指示为下地壳底侵玄武岩石部分熔融的产物,源区残留矿物有角闪石+石榴子石,具Cu-Au矿的成矿潜力；(3)中二叠世石英闪长岩(261.8±1.5Ma)富Na贫K,拉斑-钙碱性系列,属Ⅰ型花岗岩；高Sr高Y、Yb,富集Ba、Rb、Th、U、K、La、Sr、Ce、Sm、Zr-Hf,相对亏损Nb、Ta、P、Ti,δEu=0.87,说明花岗岩浆源区可能具下地壳性质,残留矿物可能既有斜长石又有石榴子石,不具Cu-Au和W-Sn的成矿潜力；(4)晚二叠世二长花岗岩(252.0±2.1Ma)富Na贫K的钙碱性-高钾钙碱性系列,低Sr高Y,富集Rb、Th、U、K、Zr-Hf和LREE,相对亏损Ba、Nb、Ta、P、Ti,δEu平均为0.62,(87Sr/86Sr) I:0.705968-0.706571,(143Nd/144Nd)I=0.512393-0.512404,εNd(t)=+1.89479和+1.69254。总体特征显示花岗岩源岩为新生地壳,部分熔融深度较浅,源区残留斜长石和角闪石,具有W-Sn成矿潜力；(5)中二叠世英云闪长斑岩(262.2±1.4Ma)属高钾钙碱性系列,A/CNK>1.1(1.11-1.34)和A/CNK<1.1(0.99-1.06),分属S型和Ⅰ型,部分样品(Ga/Al)×104>2.6,为A型；低Sr低Yb,大多与我国喜马拉雅地区的淡色花岗岩类似；富集Rb、Th、U、K、Zr-Hf和LREE,相对亏损Ba、Nb、Ta、Sr、P、Ti,δEu=0.42-0.89；Sr-Nd同位素组成可分为两组地球化学端元：一是略富集的Sr-Nd同位素组成,(87Sr/86Sr)I=0.706211-0.706309,(143Nd/144Nd)I=0.512342-0.512344；二是高度富集的,(87Sr/86Sr)I达到0.729009-0.732882,(143Nd/144Nd)I=0.511861-0.511899,εNd(t)<0(-8.55910和-7.80714),表明源于不均一性的下地壳物质,应为含有斜长石-角闪石-石榴子石-辉石的高压麻粒岩部分熔融形成的,岩浆活动有利于Cu-Au矿成矿作用：5)通过对英云闪长斑岩与其蚀变形成的绢英岩地球化学和氧同位素对比研究认为,参与蚀变过程的流体(热液)为英云闪长岩浆晚期的热液,并非有其它的流体(热液)参与：6)在晚古生代中-晚期研究区发生两次重要的后造山挤压-伸展转换阶段及相应的花岗岩浆-成矿作用：晚泥盆世(369Ma)形成低Sr高Y型花岗闪长岩(YQ57-YQ63),源区深度较浅(<35Km),成矿潜力弱；中-晚二叠世花岗岩浆作用又可分为两个侵入次：在中二叠世(262Ma)形成了高Sr低Y型花岗闪长岩和低Sr低Y型英云闪长斑岩,源于加厚的下地壳(厚度>45Km)底侵玄武质岩石的部分熔融,两者均具有Cu-Au矿的成矿潜力；晚二叠世由于地壳的持续伸展拉张、减薄,下地壳物质再次在底侵玄武岩浆加热作用下发生部分熔融形成了具有W-Sn成矿潜力的二长花岗岩(252Ma)。并据此建立了研究区花岗岩成岩成矿模式,指出了该区的找矿标志。更多还原

【Abstract】 Located at the intersection between Altun and Southern Qilian tectonic belts, Huashigou Copper ore region contains late Paleozoic granitic magmatism and the related Cu-Au ore and W-Sn mineralized spots. The origins and mineralization of the granitic rocks in the studied area have not been studied systematically for a long time, so that the great development in ore-prospecting has not been made. Based on advance in the research of granites and mineralization, this paper is in the point of the scientific thoughts of tectonic plate theory, and by use of comprehensively studied methods of petrology, petro-geochenmistry, isotopic geochemistry and tectonics, and by the means of the modern test technology, to research tectono-magma-mineralization and tectonic geodynamic processes of the formation and ore-forming of the granites, and then to establish the granites and their metallogenic model. The creative results on the below:1) Based on the survey of field geology, together with the studied results, this paper takes Huashigou ore region to the southern margin of west end of the Southern Qilian tectonic belt, closely adjacent to the mid-Altun and northern Altun tectonic belts. Therefore, the tectono-magma-mineralization in the studied area was strictly controlled by the above two tectonic belts.2) Based on the studies of mineralogy and petrology of the granitoids, the granitoids in the studied area are classified by use of petro-chemistry, and they are granodiorite (Ⅰ-type), quartz-diorite (Ⅰ-type), toellite/porphyry (Ⅰ-and S-type), adamellite (Ⅰ-and S-type) and alterated sericite-quartz rock.3) The highly precise isotopic chronology of the zircon LA-ICP-MS U-Pb ages of the granites is first studied, and the results show that the weighted average age of granodiorite (sample No:YQ-57) distributing in the west of fault F1 in the region is 368.7±3.5 Ma, and that granodiorite (YQ-1), adamellite (YQ-25), quartz-diorite (YQ-81), toellite/porphyry (YQ-91) between faults Fl and F3, are ages of 261.1±3.8 Ma,252.0±2.1 Ma,261.8±1.5 Ma, and 262.2±1.4 Ma, respectively. Meanwhile, these indicate that two very important extensional tectono-magmatic events took place in Paleozoic period in the studied area, they are also important chronological evidence for building the regional geological framework.4) The studied results of major-, trace-, rare-earth-elements and Sr-Nd-Hf-O isotopic geochemistry show:(1) late Devonian granodiorite (368.7±3.5Ma) is high-K calc-alkaline series, has high-Sr and low-Y (Yb) contents, obviously enriched with Rb, K, Th, Zr-Hf and LREE, relatively depleted in Ba, Nb, Ta, Sr, P, Ti, andδEu= 0.64-0.89; greatly high (87Sr/86Sr), (0.712261-0.712614) and low (143Nd/144Nd)I (0.511838-0.511825), (176Hf/177Hf)I= 0.282487, negativeδNd(t) values (-6.748~-6.989) andδHf(t) (-2.334), characteristic of the highly enriched source rocks with residual minerals of plagioclase+ homblende+pyroxene, and lower differentiation of the magma; (2) Mid-Permian granodiorite (261.1±3.8Ma) dues to calc-alkalineⅠ-type granite, has high-Sr and low-Y (Yb) contents, rich in Rb, Th, U, K, Sr, Zr-Hf and LREE, relatively depleted in Ba, Nb, Ta, P, Ti, and averageδEu value equal to 0.83; (87Sr/86Sr) I= 0.706963-0.706571, (143Nd/144Nd)I=0.512246-0.512266,δNd(t)=-1.23847 and -0.84907, (176Hf/177Hf)1=0.282766, and highδ18OV-smow values (12.1-12.5‰), indicating that the rocks originated from the partial melting of the underplating basaltic rocks, and relic minerals of hornblende+garnet, and that have good Cu-Au metallogenic potentiality; (3) Mid-Permian quartz-diorite (261.8±1.5Ma) is low-K to calc-alkalineⅠ-type, rich in Na, Ba, Rb, Th, U, K, La, Sr, Ce, Sm and Zr-Hf, depleted in Nb, Ta, P, Ti, and averageδEu value equal to 0.87, showing the granitic magma originated from lower crust, has no Cu-Au and W-Sn metallogenic potentiality; (4) late Permian adamellite (252.0±2.1Ma) is calc-alkaline to high-K calc-alkaline series with high-Na and-Y and low-K and-Sr, enriched relatively with Rb, Th, U, K, Zr-Hf and LREE, depleted in Ba,Nb,Ta,P and Ti, and averageδEu value equal to 0.62; (87Sr/86Sr)1,= 0.705968-0.706571, (143Nd/144Nd)I=0.512393-0.512404,εNd(t)=+1.89479 and +1.69254, having characteristic of the source rocks of juvenile crust at relatively shallow level with residual minerals of hornblende+plagioclase, and W-Sn metallogenic potentiality; (5) Mid-Permian toellite/porphyry (262.2±1.4Ma) dues to high-K calc-alkaline series, has two groups of A/CNK>1.1 and A/CNK<1.1, is S- and I-types, respectively, some due to A-type with (Ga/Al)×104>2.6; has low-Sr and -Yb, characteristic of the Miocene leucogranites in higher Himalaya; and enriched relatively with Rb, Th, U, K, Zr-Hf and LREE, depleted in Ba、Nb、Ta、Sr、P、Ti, andδJEu=0.42-0.89; Sr-Nd isotopic composition may be divided into two groups:one is slightly enriched Sr-Nd isotopic composition, (87Sr/86Sr)I=0.706211-0.706309, (143Nd/144Nd)I= 0.512342-0.512344, and the other highly enriched, (87Sr/86Sr)I= 0.729009-0.732882, (143Nd/144Nd)I=0.511861-0.511899, andδNd(t)<0(-8.55910 and -7.80714), showing that the rocks originated from the partial melting of high pressure granulite of the heterogeneous lower crust with minerals of plagioclase+hornblende+garnet+pyroxene, having Cu-Au mineralization.5) Compared studies of geochemistry andδ18O of gsericite-quartz rock with toellite/porphyry, this paper points out that the fluids in the alteration-were from the hydrothmermal solution of the late toellitic magmas, not from the other fluids.6) Two important granitic magmatic events took place in the region responding to post-orogenic compression-extensional transform periods during Paleozoic:the magmatic source of late Devonian granodiorites (YQ-57-YQ-63,369Ma) with low-Sr and high-Y(Yb) contents located at relatively shallow levels (ca.< 35Km) of continental crust, so they have little metallogenic potentiality; mid-late Permian granitic magmatasm may be divided into two epochs of intrusion:the granodiorites with high-Sr and low-Y contents, and toellite/porphyry with low-Sr and-Y (Yb) formed at 262Ma, and resulted from partial melting of the underplating basaltic rocks of thickened lower crust (>45Km), have good Cu-Au metallogenic potentiality; late Permian adamellite (252Ma) with W-Sn metallogenic capacity originated from partial melting of thinned lower crust due to the long extension of the crust during the late Permian. According to the results, the diagenetic and metalogenic models of the granitoids in the region are scientifically established, and the direction of ore-prospecting is also pointed out.更多还原