东天山红山铜金矿床氧化带硫酸盐矿物的系列发现.doc

东天山红山铜金矿床氧化带硫酸盐矿物的系列发现、形成时限、机理及意义 许英霞 秦克章 丁奎首 中国科学院矿产资源研究重点实验室，中国科学院地质与地球物理研究所，北京100029 东天山红山、梅岭铜-金矿床为卡拉塔格铜-金成矿带上所新发现的两个铜-金矿床之一，在大地构造位置上处于大南湖–突苏泉晚古生代岛弧带北段的中生代上叠火山盆地。红山矿区容矿岩主要为流纹英安质火山碎屑岩，矿化与石英斑岩、流纹斑岩、次花岗斑岩密切相关（秦克章等，2001，2006）。围岩蚀变主要为硅化、绢云母化、伊利石化、粘土化、明矾石化、叶蜡石化和绿泥石化。铜、金矿化主要呈细脉浸染状和细脉状，偶见网脉状。该矿床处于东天山极端干旱少雨且稳定的荒漠地带，是东天山最炎热的地区之一，最高温度达到60℃，现年降水量平均只有34.1mm，干旱少雨和极大的蒸发作用造成其氧化带极其发育，厚达5060m，产有一系列复杂罕见的硫酸盐矿物，并且以硫酸盐矿物为主。 通过对本矿床火山–次火山岩石组合、热液蚀变组合及矿石结构构造与矿化类型研究得出，红山铜-金矿床为高硫型浅成低温与斑岩型铜金矿之间的过渡类型，相当于福建紫金山式；构造、地层、岩浆活动与火山机构热液蚀变为主要控矿因素，金矿化作用在空间上与火山机构、次火山岩相－石英斑岩、流纹斑岩及热液活动形成过程的微细粒黄铁矿化有关，铜矿化与石英斑岩及热液爆破角砾岩有关（秦克章等，2001；方同辉等，2002；许英霞等，2006，2007）。通过目前竣工的4个钻孔岩芯矿化蚀变情况和激电剖面、激电测深以及Eh-4剖面资料分析表明红山矿床深部450m以下可能存在有隐伏的斑岩体，因此在卡拉塔格成矿带上具有寻找大型浅成低温热液-斑岩Au-Cu矿床的潜力。 在野外工作的基础上，通过XRD、TA和湿法化学等方法对红山铜-金矿床氧化带作了系统研究，识别出23种硫酸盐矿物（许英霞等，2006，2007），且高铁叶绿矾、铜叶绿矾、板铁矾、副基铁矾、钾铁矾、斜钾铁矾、变纤钠铁矾、柱钠铜矾和副针绿矾9种系在我国首次发现，副针绿矾矿物为世界上继智利后的第二次报道。通过对8种硫酸盐矿物的穆斯堡尔谱分析和6种硫酸盐矿物的红外光谱分析，确定了矿物中铁的氧化态和配位数以及不同基团的存在，进一步保证了硫酸盐矿物系列研究的准确性。对呈多型的针绿矾和副针绿矾的电子探针分析表明，在其环状生成过程中，不仅堆垛层错起着主导作用，Al杂质在矿物晶格中有规律的分布亦为重要因素之一。 红山矿床具有代表性蚀变矿化的原生硫化物样品的δ34S值为1.86‰5.69‰，平均值为3.70‰；氧化带八种硫酸盐矿物的δ34S值变化在2.15～6.73‰之间，平均值为3.74‰，与本矿床原生硫化物的δ34S值非常接近，说明该矿床的硫源主要来自深源岩浆热液流体，硫酸盐继承了母体硫化物的同位素组成，且后期形成的高铁硫酸盐和早期结晶的低铁硫酸盐的δ34S值变化不明显，因此推测硫酸盐矿物的形成是一个结晶、沉淀、再结晶的多期次重复的漫长过程。氧化带形成大量硫酸盐的过程中，除黄铁矿和黄铜矿外，源源不断从地面喷出的热泉和从火山口喷气孔喷发后覆盖在表层的自然硫对其提供了水介质和S元素。 通过对矿床中黄铁矿和黄铜矿样品的电子探针分析，其Co/Ni比值0.98～34.72，大部分集中在5左右，说明红山铜-金矿床是一个典型的陆相火山成因岩浆热液矿床；且Au与Ag、Zn、Te、Bi呈正相关，Cu与Hg、Se、Sb呈正相关，说明金、铜没有处于同一矿化簇团的矿化因子中。氧化带中金的富集主要原因是氧化还原电位的改变、pH的改变和金的可溶性络合物易被吸附。 对卡拉塔格成矿带的三期石英闪长岩－黑云母花岗岩－二长花岗岩，测得其角闪石、黑云母K-Ar年龄在296.536.69Ma、231.993.45Ma、217.106.41Ma，区间为296Ma～217Ma，相当于晚石炭世末－三叠纪产物。且由于含矿火山岩含有花岗岩的角砾，表明其形成明显晚于上述花岗岩，即与成矿密切相关的火山-次火山岩晚于晚三叠纪，为中生代的产物（秦克章等，2006；许英霞，2007，博士论文）。东天山区域上的三亚、白石泉花岗岩、红柳构花岗岩年龄（秦克章等，2006）以及白山钼矿获得辉钼矿铼-锇同位素等时线年龄（Zhang et al., 2005）均为三叠纪，表明东天山地区的确存在中生代火成成岩成矿事件。 我们首次尝试对氧化带中三种含钾的硫酸盐矿物进行了K-Ar年龄测试，结果表明赋存在氧化带下部1m的绿钾铁矾K-Ar年龄为56.023.98Ma，位于氧化带下部1.5m的高铁叶绿矾的K-Ar年龄为8.621.12Ma，位于氧化带下部14m的斜钾铁矾K-Ar年龄为4.070.39Ma，位于氧化带下部10m的绿钾铁矾K-Ar年龄为14.731.73Ma，因此红山铜-金矿床氧化带生成年龄分布在60～3.38Ma之间；通过与不同类型矿床氧化带年龄对比，确认氧化带的风化氧化作用主要发生在新生代（65Ma以来）。而新生代以来全球构造事件与气候变化事件的耦合对地球表层系统的影响，同样会作用于矿床表层氧化带。现初步推断认为，上述年龄与印度-亚洲大陆碰撞及随后青藏高原的多期幕式隆升不谋而合，系青藏高原碰撞隆升远程效应的表现和记录，古新世/始新世极热事件（PETM）时期全球性大幅度增温所导致地表堆积层化学风化作用的加强是1m深度绿钾铁矾含钾量突增的原因之一。氧化带1.5m深度的高铁叶绿矾（绝对年龄8.621.12Ma）较低的钾含量（0.28）则是由于8Ma左右的全球性的气候变干冷所致。前人对于PETM事件的研究主要依赖于生物群、同位素和磁化率等参数，本研究初步提出了使用不同种类硫酸盐矿物作为气候变化替代指标的可能。 关键词高硫型浅成低温热液矿床，氧化带，K-Ar、Ar-Ar定年，S同位素，穆斯堡尔谱， 红外光谱，多型性，红山铜-金矿床，卡拉塔格，极端干旱区，东天山 Series Discovery of Sulfate Minerals, ation Duration and Mechanism of Oxidization Zone in Hongshan HS-epithermal Cu-Au Deposit, Eastern Tianshan, and Their Significance Xu Yingxia, Qin Kezhang and Ding Kuishou Key Lab. of Mineral Resources, Institute of Geology and Geophysics, CAS, Beijing 100029 Located in the Paleozoic uplift along the southern margin of Tu-Ha basin in eastern Xinjiang, the newly discovered Hongshan and Meiling Cu-Au deposits occur in the superimposed Kalatage Mesozoic volcanic basin upon the north section of later Paleozoic Dananhu-Tousuquan accretionary arc Qin et al., 2001,2006. Kalatage Cu-Au orebelt is controlled by NWW-trend faults. The host rocks of Hongshan ore district are mainly rhyolitic-dacitic ignimbrites, whereas Cu-Au mineralization is closely related to quartz porphyry, rhyolitic porphyry and granitic porphyry. Mineralization styles are dominantly veinlet-disseminated and veinlet, occasionally stockwork. The mineral association is chalcopyrite, pyrite, bornite, chalcocite and sphalerite. The hydrothermal alteration consists of silicfication, sericitization, illitization, hydromuscovitization, alunitization, pyrophylitization, and chloritization. Hongshan Cu-Au deposit, on the edge of the desert, is one of the driest areas in eastern Tianshan. Moreover, the highest temperature can be up to 60℃, and the average rainfall receives only 34.1mm/y. The light rainfall and rapid evaporation in the vicinity of this deposit have allowed the ation of a great variety of water-soluble sulfates. Oxidization zone of this deposit lies on the upper part of primary sulfide orebody appearing with a depth of 50-60m, which is dominant in sulfate minerals. Based on the field observation, the volcanic and sub-volcanic rock composition, hydrothermal alteration, ore structure and mineralization characteristics, this paper proposed that the Hongshan Cu-Au deposit belongs to a transitional type from high-sulfide epithermal to porphyry Cu-Au deposit, which corresponds with the typical HS-epithermal deposit such as Zijinshan Au-Cu deposit in Fujian Province, SE-China. The tectonic, stratum, magmatism and volcanic apparatus control the ore ation, whereas Au mineralization is closely related to quartz porphyry, rhyolitic porphyry and fine grained pyritization in hydrothermal activity, and Cu mineralization is closely related to quartz porphyry and hydrothermal explosive breccias Qin et al., 2001; Fang et al., 2002; Xu et al., 2006, 2007. The alteration and mineralization features of four bore cores, induced activity polarization well logging and Eh-4 geophysical section, deep mineralization anomaly objects of orebody shows the existing of concealed porphyry orebody below 450m. Therefore, it is great potential that large HS-style epithermal-porphyry Au-Cu deposit will be found in Hongshan ore district and even in the whole Kalatage metallogenetic belt. 23 sulfate minerals were identified in this work in Oxidation zone of Hongshan Cu-Au deposit. The results of samples XRD and chemical analysis were furthermore confirmed through thermal, infrared spectrum and mssbauer spectrum analysis Xu et al., 2006, 2007. Among those, nine minerals as Ferricopiapite, Cuprocopiapite, Rhomboclase, Parabutlerite, Krausite, Yavapaiite, Metasideronatrite Kroehnkite and Paracoquimbite were founded in China for the first time. And Paracoquimbite was reported in the world for the second time since initially reported at 1938 in Chile. EPMA analysis shows that Al impurity in crystal lattice is important to polytype ation of paracoquimbite and coquimbite besides stack fault. Sulfur isotope analyses show the δ34S values of pyrites vary in the range of 1.86‰－5.69‰, with an average of 3.70‰, mostly in the range of 1.86‰－3.20‰. The δ34S values of sulfates vary in the range of 2.15‰－6.73‰ in oxidation zone, with an average of 3.74‰, mostly equals as δ34S values of primary sulfides in Hongshan Cu-Au deposit. So supergene sulfates inherit sulfur of primary hydrothermal sulfides. The δ34S values are mostly the same in different sulfates in oxidation zone. As well as pyrite and chalcopyrite, volcanic hot spring and associated native sulfur underground also provide water medium and sulfur during the ation process of sulfate. According to the EPMA of sample chalcopyrite and pyrite in Hongshan deposit, the value of Cu/Ni is 0.98-34.72, mostly close to the value of 5, which shows that Hongshan deposit is a typical subaerial volcanogenic magmatic hypothermal deposit. Au and Ag, Zn, Te and Bi are positive correlation, Cu and Hg, Se, Sb are positive correlation, indicates Au and Cu don’t locate in the factor of mineralization of same mineralization groups. The reasons of gold concentration in the oxidation zone include change of redox potential Eh and PH, soluble complex and colloid of gold adsorbed easily. The biotite and hornblende K-Ar isotopic ages from the wall rockquartz diorite, biotite granite and monzonite granite are 231.993.45Ma, 237.972.36Ma and 296.536.69Ma respectively. The ore-bearing rhyolitic breccia lava contains breccia of the biotite granite that indicates the volcanism and related Cu-Au mineralization occurred later than the granite, possibly in Mesozoic. K-Ar ages of granitoids in Sanya, Baishiquan and Hongliugou area Qin et al., 2006; Xu, 2007, PhD Thesis and Molybdenite Re-Os age of Baishan Mo deposit Zhang et al., 2005 all are in Triassic. Besides late Paleozoic magmatism Rui et al., 2002; Qin et al., 2002, 2003; Li et al., 2004, igneous magmatic event of Mesozoic was widespread in eastern Tianshan. The K-Ar age dating indicates that the K-Ar age of Voltaite occurred below surface 1m is 56.023.98Ma, K-Ar age of Ferricopiapite occurred below surface 1.5m is 8.621.12Ma, K-Ar age of Yavapaiite occurred below surface 14 m is 4.070.39Ma, and K-Ar age of Voltaite occurred below surface 10 m is 14.731.73Ma. So the age interval of oxidation zone of Hongshan copper-gold deposit is between 60 -3.38Ma. Oxidization occurred at Caenozoic era from 65Ma, which can be identified through comparing with different deposits oxidation zone in other countries. The coupling between global tectonic event and climatic change event, which occur from Caenozoic era, has some effect on epigeosphere system, which can act on the surface of bed oxidation zone similarly. It induces that the age mentioned above coincide with collision of India-Asia and multistage uplifting of Qinhai-Tibet Plateau happened subsequently. Bed oxidation zone is the effect and record of collision and uplifting of Tibet Plateau. The strong chemical weathering of surface accumulation to which was leaded by PETM event occurred Paleocene and Eocene is the reason of Voltaite sharply increased. On the contrary, Ferricopiapite was ed in the global cold weather. The predecessor did much research through biota, isotopes, susceptibility, but this paper try to use different sulfate mineral instead of climatic change. So the research of sulfate minerals not only indicates a great deal of oxidized zone feature, but also the intergrowth of sulfate minerals may be used to trace paleoenviroment and paleoclimate of oxidation zone. Key words HS-epithermal deposit, oxidation zone, K-Ar and Ar-Ar age dating, S isotope, Mssbauer spectra, Infrared spectrum, polytypism, Hongshan Cu-Au deposit, Kalatage ore belt, hyper-arid area, eastern Tianshan 5