海南省抱伦金矿变质基性岩成因及与金成矿作用关系
发布时间：2018-09-09 18:17
【摘要】：抱伦金矿位于海南省西南部,东西向尖峰-吊罗断裂和九所-陵水断裂之间,北东向白沙断裂的西侧,是目前海南省规模最大的高品位金矿床。抱伦金矿是典型的石英脉型金矿,矿体受矿区豪岗岭背斜和发育在背斜核部的NNW向断裂破碎带控制。在对海南省抱伦金矿进行研究的过程中,我们在矿井中发现大量的变质基性岩和金矿脉在空间上紧密伴生。本文结合前人对矿床的研究,在野外地质调查的基础上,开展了岩相学和成因矿物学研究、全岩地球化学和Sm-Nd同位素组成分析、以及SHRIMP锆石U-Pb定年,并结合全岩金丰度分析,探讨了变质基性岩的岩浆源区特征和产出构造环境,以及这些基性岩与抱伦金矿的成矿作用关系,取得的主要成果和认识如下:(1)根据野外产状和地球化学特征,变质基性岩可以分为两组。在野外产状方面,第一组呈细脉状产出,与地层、石英脉混杂,局部可见石英和地层透镜体;第二组变质基性岩脉较宽、延伸大,脉体较干净。在地球化学特征上,第一组样品的REEs含量较高,为球粒陨石的20~80倍,且表现出强烈的LREE富集和Eu的负异常(但BL-065和13BL-87有轻微正异常),相对于N-MORB富集Th、Ta、Nb和Ce,在蛛网图上形成中间“隆起”,εNd(230Ma)值大多处于-6.62~-4.45之间;第二组样品的REEs含量相对较低,为球粒陨石的14~40倍,大多表现出LREE亏损的稀土配分模式(13BL-44除外)和Eu的正异常(但13BL-71有轻微负异常),且相对N-MORB富集Sr、K、Rb和Ba等LIL元素和Th,LIL/HFS比值高,εNd(230Ma)值分布于0.33~5.65之间。两组变质基性岩的主要硅酸盐矿物都为斜长石和角闪石,主要金属矿物为磁铁矿、黄铁矿和黄铜矿。第一组变质基性岩中有石英出现,局部亦出现碳酸盐,金属矿物还有少量闪锌矿;第二组变质基性岩中局部可见残留辉石和蚀变矿物绿泥石、绿帘石、黝帘石、绢云母、黑云母和碳酸盐等。(2)地球化学特征表明,第一组样品的岩浆源区尽管也是亏损地幔源区,但主要受到的是富集地幔源区的混染,同时有少量地壳成分的加入,几乎未受到过俯冲带含水流体的影响。两组样品的岩浆源区均较浅,源区没有石榴石相的残余;而第二组样品的岩浆源区可能是受到过俯冲带含水流体影响的亏损地幔源区,具有岛弧岩浆的性质,几乎未受到过富集岩石圈地幔的影响,可能受到过少量地壳的混染。第一组样品形成于以分离结晶为主的岩浆演化过程,分离结晶的矿物组合是单斜辉石+斜长石±橄榄石;第二组样品形成于以部分熔融为主的岩浆演化过程。(3)通过挑选变质基性岩中的锆石进行SHRIMP U-Pb定年,获得第二组变质基性岩的成岩年龄为231.6±2.6Ma,此年龄和尖峰岩体的成岩年龄208~249Ma、抱伦金矿的成矿年龄224.6±7.2Ma相近。而且,在地理位置上,本次研究的变质基性岩和尖峰岩体也相邻。结合变质基性岩的地球化学特征和尖峰岩体构造环境的研究成果推断,变质基性岩产出于后碰撞阶段伸展的构造环境。根据变质基性岩的地球化学特征和年代学特征,综合前人对华南构造背景的研究,古特提斯洋东段在海南岛闭合时,洋壳自北向南俯冲进入南部块体之下,并于208~249Ma左右处于后碰撞阶段。(4)变质基性岩的金丰度分析结果表明,第二组变质基性岩中部分样品的金丰度远远高于地壳克拉克值,且数据离散度大,显示出Au自变质基性岩中被活化、迁移的迹象。地球化学特征表明,第二组变质基性岩的岩浆是Au运移的合适载体。地质年代学结果显示,变质基性岩的成岩年龄和抱伦金矿的成矿年龄在误差范围内一致。因此,第二组变质基性岩可能在成矿作用中提供了Au。(5)综合以上分析,抱伦金矿变质基性岩产出和金成矿的模型应为:后碰撞构造环境下,两种变质基性岩先后依次产出。其中,发育较晚的一组基性岩将成矿物质Au从深部携带到浅部后,其基性岩浆热液携带着Au等成矿元素和尖峰岩体的酸性岩浆热液混合,并沿着裂隙运移上升。志留系陀烈组的含碳千枚岩和从地表渗下的天水使成矿流体的化学性质发生改变,Au富集成矿。(6)本文的研究表明,抱伦金矿成矿的时间对应着造山运动的后碰撞阶段以及从挤压向伸展转换的应力机制。相邻的尖峰-吊罗断裂应为切穿大陆岩石圈的深大断裂。结合前人研究成果,抱伦金矿应为造山型金矿。
[Abstract]:Baolun gold deposit is located in the southwest of Hainan Province, between the East-West spike-suspension fault and Jiusuo-Lingshui fault, and on the west side of the north-east Baisha fault. It is the largest high-grade gold deposit in Hainan Province at present. Control. During the study of Baolun gold deposit in Hainan Province, we found a large number of metamorphic basic rocks and gold veins closely associated in space. Based on the previous study of the deposit and on the basis of field geological survey, this paper carried out lithofacies and genetic mineralogy, whole rock geochemistry and Sm-Nd isotope composition. Based on the analysis and SHRIMP zircon U-Pb dating, and combined with the analysis of the whole rock gold abundance, the magmatic source area characteristics and occurrence tectonic setting of metamorphic basic rocks, and the relationship between these basic rocks and the mineralization of the Baolun gold deposit are discussed. The main achievements and understandings are as follows: (1) According to the field occurrence and geochemical characteristics, metamorphic basic rocks can be divided into metamorphic basic rocks. In the field occurrence, the first group occurs as fine veins, intermingled with strata, quartz veins, locally visible quartz and stratigraphic lenses; the second group metamorphic basic dikes are wider, larger, and more clean. In geochemical characteristics, the REEs content of the first group is 20-80 times higher than that of chondrites, and shows strong LREE enrichment. Negative anomalies with Eu (but slightly positive anomalies with BL-065 and 13BL-87), compared with N-MORB enrichment of Th, Ta, Nb and Ce, formed an intermediate "uplift" on the cobweb, and the values of epsilon Nd (230Ma) were mostly between - 6.62 and - 4.45; the second group of samples had relatively low REEs content, 14-40 times that of chondrites, mostly showing LREE depletion patterns (13BL-44). Except for positive anomalies (but slightly negative anomalies in 13BL-71) and Eu, the LIL elements such as Sr, K, Rb and Ba are enriched and the ratio of LIL to HFS is high relative to N-MORB, and the value of epsilon Nd (230 Ma) is distributed between 0.33 and 5.65. The main silicate minerals of the two groups of metamorphic basic rocks are plagioclase and amphibole, and the main metal minerals are magnetite, pyrite and chalcopyrite. Quartz appears in the metamorphic basic rocks, carbonate occurs locally, metallic minerals and a small amount of sphalerite. Residual pyroxene and altered minerals such as chlorite, epidote, epidote, sericite, biotite and carbonate can be found locally in the metamorphic basic rocks of the second group. (2) Geochemical characteristics show that although the magma source area of the first group is also deficient. The source area of the two groups of samples is shallow, and there is no residual garnet facies in the source area. The source area of the second group of samples may be affected by the water-bearing fluid in the subduction zone. The first group of samples were formed during the magmatic evolution process dominated by separation crystallization, and the mineral assemblage of separation crystallization was clinopyroxene + plagioclase + olivine. (3) By selecting zircons from metamorphic basic rocks for SHRIMP U-Pb dating, the diagenetic age of the second group of metamorphic basic rocks is 231.6+2.6 Ma, which is similar to the diagenetic age of the Jianfeng pluton from 208 to 249 Ma, and the metallogenic age of the Baolun gold deposit from 224.6+7.2 Ma. According to the geochemical characteristics of metamorphic basic rocks and the tectonic setting of the spikes, it is inferred that the metamorphic basic rocks occurred in the extensional tectonic environment during the post-collision stage. When the eastern segment of the Paleo-Tethys Ocean closed in Hainan Island, the oceanic crust subducted from north to South and entered the southern block, and was in the post-collision stage around 208-249 Ma. (4) The gold abundance analysis of metamorphic basic rocks shows that the gold abundance of some samples in the second group of metamorphic basic rocks is much higher than that of the crustal Clark value, and the data dispersion is large. Geochemical characteristics show that the magma of the second group of metamorphic basic rocks is an appropriate carrier for Au migration. Geochronological results show that the diagenetic age of metamorphic basic rocks is consistent with the metallogenic age of the Baolun gold deposit within the error range. Au. (5) Based on the above analysis, the model of occurrence of metamorphic basic rocks and gold mineralization in Baolun gold deposit should be that two metamorphic basic rocks occur successively under post-collision tectonic environment. Among them, a group of late-developed basic rocks carry Au from deep to shallow, and their basic magmatic hydrothermal fluid carries Au and other metallogenic elements and Au. The acidic magmatic hydrothermal mixtures of the Jianfeng intrusion migrate and rise along the fissures. The chemical properties of the ore-forming fluids are changed by the carbonaceous phyllite of the Silurian Tuoli Formation and the Tianshui percolated from the earth's surface. Au enrichment and mineralization occur. (6) This study shows that the metallogenic time of the Baolun gold deposit corresponds to the post-collisional stage of orogeny and the compressional direction. The adjacent peak-slip faults should be deep and large faults cutting through the continental lithosphere, and the Baolun gold deposit should be an orogenic gold deposit in combination with previous research results.
【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.51
本文编号：2233187
[Abstract]:Baolun gold deposit is located in the southwest of Hainan Province, between the East-West spike-suspension fault and Jiusuo-Lingshui fault, and on the west side of the north-east Baisha fault. It is the largest high-grade gold deposit in Hainan Province at present. Control. During the study of Baolun gold deposit in Hainan Province, we found a large number of metamorphic basic rocks and gold veins closely associated in space. Based on the previous study of the deposit and on the basis of field geological survey, this paper carried out lithofacies and genetic mineralogy, whole rock geochemistry and Sm-Nd isotope composition. Based on the analysis and SHRIMP zircon U-Pb dating, and combined with the analysis of the whole rock gold abundance, the magmatic source area characteristics and occurrence tectonic setting of metamorphic basic rocks, and the relationship between these basic rocks and the mineralization of the Baolun gold deposit are discussed. The main achievements and understandings are as follows: (1) According to the field occurrence and geochemical characteristics, metamorphic basic rocks can be divided into metamorphic basic rocks. In the field occurrence, the first group occurs as fine veins, intermingled with strata, quartz veins, locally visible quartz and stratigraphic lenses; the second group metamorphic basic dikes are wider, larger, and more clean. In geochemical characteristics, the REEs content of the first group is 20-80 times higher than that of chondrites, and shows strong LREE enrichment. Negative anomalies with Eu (but slightly positive anomalies with BL-065 and 13BL-87), compared with N-MORB enrichment of Th, Ta, Nb and Ce, formed an intermediate "uplift" on the cobweb, and the values of epsilon Nd (230Ma) were mostly between - 6.62 and - 4.45; the second group of samples had relatively low REEs content, 14-40 times that of chondrites, mostly showing LREE depletion patterns (13BL-44). Except for positive anomalies (but slightly negative anomalies in 13BL-71) and Eu, the LIL elements such as Sr, K, Rb and Ba are enriched and the ratio of LIL to HFS is high relative to N-MORB, and the value of epsilon Nd (230 Ma) is distributed between 0.33 and 5.65. The main silicate minerals of the two groups of metamorphic basic rocks are plagioclase and amphibole, and the main metal minerals are magnetite, pyrite and chalcopyrite. Quartz appears in the metamorphic basic rocks, carbonate occurs locally, metallic minerals and a small amount of sphalerite. Residual pyroxene and altered minerals such as chlorite, epidote, epidote, sericite, biotite and carbonate can be found locally in the metamorphic basic rocks of the second group. (2) Geochemical characteristics show that although the magma source area of the first group is also deficient. The source area of the two groups of samples is shallow, and there is no residual garnet facies in the source area. The source area of the second group of samples may be affected by the water-bearing fluid in the subduction zone. The first group of samples were formed during the magmatic evolution process dominated by separation crystallization, and the mineral assemblage of separation crystallization was clinopyroxene + plagioclase + olivine. (3) By selecting zircons from metamorphic basic rocks for SHRIMP U-Pb dating, the diagenetic age of the second group of metamorphic basic rocks is 231.6+2.6 Ma, which is similar to the diagenetic age of the Jianfeng pluton from 208 to 249 Ma, and the metallogenic age of the Baolun gold deposit from 224.6+7.2 Ma. According to the geochemical characteristics of metamorphic basic rocks and the tectonic setting of the spikes, it is inferred that the metamorphic basic rocks occurred in the extensional tectonic environment during the post-collision stage. When the eastern segment of the Paleo-Tethys Ocean closed in Hainan Island, the oceanic crust subducted from north to South and entered the southern block, and was in the post-collision stage around 208-249 Ma. (4) The gold abundance analysis of metamorphic basic rocks shows that the gold abundance of some samples in the second group of metamorphic basic rocks is much higher than that of the crustal Clark value, and the data dispersion is large. Geochemical characteristics show that the magma of the second group of metamorphic basic rocks is an appropriate carrier for Au migration. Geochronological results show that the diagenetic age of metamorphic basic rocks is consistent with the metallogenic age of the Baolun gold deposit within the error range. Au. (5) Based on the above analysis, the model of occurrence of metamorphic basic rocks and gold mineralization in Baolun gold deposit should be that two metamorphic basic rocks occur successively under post-collision tectonic environment. Among them, a group of late-developed basic rocks carry Au from deep to shallow, and their basic magmatic hydrothermal fluid carries Au and other metallogenic elements and Au. The acidic magmatic hydrothermal mixtures of the Jianfeng intrusion migrate and rise along the fissures. The chemical properties of the ore-forming fluids are changed by the carbonaceous phyllite of the Silurian Tuoli Formation and the Tianshui percolated from the earth's surface. Au enrichment and mineralization occur. (6) This study shows that the metallogenic time of the Baolun gold deposit corresponds to the post-collisional stage of orogeny and the compressional direction. The adjacent peak-slip faults should be deep and large faults cutting through the continental lithosphere, and the Baolun gold deposit should be an orogenic gold deposit in combination with previous research results.
【学位授予单位】：中国科学院研究生院(广州地球化学研究所)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.51
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