KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 吐拉苏盆地高硫型浅成低温热液成矿系统的形成与保存 | |
| Alternative Title | Formation and preservation of high-sulfidation epithermal system in the Tulasu basin |
| 叶甜 | |
| Subtype | 博士 |
| Thesis Advisor | 李诺 |
| 2020-09-30 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Discipline | 工学博士 |
| Keyword | 吐拉苏盆地 浅成低温热液矿床 高硫型 矿床成因 矿床保存 Tulasu basin epithermal deposit high-sulfidation deposit genesis deposit preservation |
| Abstract | 浅成低温热液型矿床是 Au， Cu， Zn 和 Pb 的重要来源，大约 12%的 Au 来自于该类矿床。该矿床具有储量大、埋藏浅、易开采的特点， 可细分为高硫型和低硫型。其中，高硫型浅成低温热液矿床常与深部斑岩型矿床具有密切的时空和成因联系，一直以来都是国内外矿床学研究的热点。吐拉苏盆地地处西天山北段伊犁地块北缘，是目前新疆最大的浅成低温热液金矿集中区，已知浅成低温热液矿床以低硫型为主。京希-伊尔曼得金矿是区内唯一的疑似高硫型浅成低温热液矿床，但因缺乏典型高硫型特征矿物而受质疑。为解决这一争议，本论文在野外地质调查基础之上，对京希-伊尔曼得金矿开展了详细的岩相学、矿物学、地球化学和年代学研究，以期准确厘定矿化作用类型，促进对吐拉苏盆地浅成低温热液矿床成矿规律和矿床保存的认识，为找矿勘探和资源潜力评价提供有益的参考和借鉴。京希-伊尔曼得金矿位于吐拉苏盆地北缘，赋矿地层为大哈拉军山组砾岩段和酸性凝灰岩段，矿体分布形态多呈地毯式、缓倾斜产出，受北西向、南北向、东西向和北东向断裂控制。围岩蚀变包括强硅化、泥化和碳酸盐化蚀变。 热液成矿阶段发育大量白铁矿（可与黄铁矿共存）， 暗示成矿流体 pH 为 3~5， 温度<240℃，氧化的热液流体， 与典型高硫型浅成低温热液矿床一致。 而矿石中常见的酸性淋滤而成多孔状石英， 亦是高硫型浅成低温热液矿床的标志性特征。为探讨其成矿过程及金沉淀机制， 本文选择主要的载金矿物——黄铁矿/白铁矿开展了详细的岩相学和矿物学研究，发现京希-伊尔曼得金矿经历了沉积成岩和热液成矿两期成矿阶段。 激光剥蚀等离子体质谱仪（LA-ICP-MS） 微区微量元素测试分析表明金主要以不可见金（固溶体）形式存在于黄铁矿和白铁矿中。早期沉积成岩阶段黄铁矿以草莓状集合体（Py0）为主， 见白铁矿以条带状他形粒状（Mrc0） 产出。前者富 Au（8.2 ~ 13.35 ppm，平均值为 12 ppm）、 As（3565 ~ 9775 ppm，平均值为 6614 ppm）， 富含 Ti， Co、 Ni、 Cu、 Zn、 Ag、 Sb 和 Pb 等微量元素， Co/Ni值为 0.006 ~ 0.52，表明其沉积成因。 后者 Au、 As 亏损， Al、 Ti 富集，含一定量的 Co、 Ni、 Cu、 Zn、 Pb 等。热液成矿阶段进一步分为：（1）面状硅化-黄铁矿化阶段，共识别出 3 种黄铁矿和 2 种白铁矿， Py1 呈疏松多孔状他形-半自形中粗粒结构， Py2 以自形-半自形板状或叶片状为主， Py3 呈浸染状自形-半自形立方体或花状集合体， 具有明显的核-幔-边结构。 Mrc1 通常与板状或叶片状黄铁矿 Py2 交代共生， Mrc2 主要呈碎裂状粗粒结构。该阶段 Au 含量相对较低， Py1至 Py3 的 Au 含量平均值分别为 0.01 ppm， 0.01 ppm 和 0.45 ppm， Mrc2 中 Au含量<0.01 ppm。与沉积成岩阶段黄铁矿 Py0 相比， 该阶段黄铁矿和白铁矿中 Co、Ni、 Zn、 Mo、 Ag 相对亏损；而 As、 Cu、 Sb、 Pb 相对富集；（2）热液角砾岩化-硅化阶段与胶状结构密切相关， Py4 通常呈细脉状、网脉状或疏松多孔状， Py5a呈浸染状、离散状他形-半自形微粒晶体或胶状结构， 发育振荡环带， Py5b 呈他形不规则致密状微细粒结构， Mrc3 呈球状或他形粒状结构， Mrc4 为黄绿色自形-半自形粒状结构， Mrc5 多呈棕色他形粒状结构。黄铁矿（Py4-Py5）和白铁矿（Mrc3-Mrc5）中 Au 含量明显升高，分别为 33.0 ppm， 1.2 ppm 和 8.7 ppm， 0.05ppm， 0.3 ppm。其他元素 Ag、 Sb、 Zn、 Pb 亦明显富集；（3）石英-碳酸盐化阶段， Py6 呈致密浸染状， 自形-半自形粒状结构，并与毒砂交代共生。 其 Au 多低于检测限。 Py6 与其它阶段黄铁矿相比， Au、 As、 Ti、 Mo、 Ag、 Sb 元素含量相对较低。大量胶状黄铁矿和白铁矿，表明成矿热液为低温热液，物理化学条件（包括氧逸度和 pH 值） 的骤变引起含矿热液过饱和，进而引起 Au 沉淀。不同阶段黄铁矿和白铁矿NanoSIMS原位微区S同位素分析为成矿流体来源和演化提供了重要信息。该矿床黄铁矿和白铁矿 δ34S 值呈现较宽的范围，为-35 ~11.5‰，但主要集中在-10 ~ 10‰。 草莓状黄铁矿较低的 δ34S 值（-35 ~ -22.9‰）可能代表了开放系统中细菌还原海相硫酸盐。 早期面状硅化-黄铁矿化阶段黄铁矿和白铁矿 δ34S 值为-13.6 ~ 9.3‰， 较宽的 δ34S 值表明硫来自于沉积地层或经分馏作用，重的 34S 进入氧化物，残余 H2S 相对贫 34S，进而导致析出硫化物 δ34S值较低。经过岩浆热液作用，硫化物经脱硫化作用和流体相互作用产生负的 δ34S值， 同时受热液流体 pH 或氧逸度的变化影响。 热液角砾岩化-硅化阶段黄铁矿和白铁矿 δ34S 值为-6.8 ~ 13.2‰，主要集中在-5 ~ 5‰之间表明硫以深源岩浆硫为主。矿区中性-酸性火山岩锆石 LA-ICP-MS U-Pb 和(U-Th)/He 年代学研究限定了火山作用与矿化作用之间的关系。详细的阴极发光（CL）图像显示锆石普遍发育核边结构， 并可细分为复杂环带结构锆石颗粒和简单环带结构锆石颗粒， 常见不规则的吸收表面和“港湾”结构。 锆石 Ti 温度计限定锆石形成温度约为 700 ~840 ℃。 锆石 U-Pb 年龄限定了两期主要的岩浆作用， 火山喷发的第一期阶段为 ~370 Ma，包括流纹岩和英安斑岩的喷出。 火山喷发的第二期为一系列交替的中性和酸性喷发单元， 凝灰岩样品中锆石年龄为 365 ~ 362 Ma。 利用最老锆石循环晶年龄（406.9 ± 5.4 Ma）和最年轻锆石（354.6 ± 3.0 Ma）估计出岩浆房持续时限长达 44 ~ 61 Ma。第一期火山岩 (U-Th)/He 年龄约为 354 ± 15 Ma，与其对应的U-Pb 年龄在一致。然而，第二期火山岩锆石颗粒(U-Th)/He 年龄中间值为 292.6 ±7.6 Ma，表明异常的长时间的热历史。进一步的锆石 LA-ICP-MS 微量元素分析表明深部镁铁矿岩浆向含矿岩浆房周期性的补给。 结合前人研究， 本文认为京希-伊尔曼得经历了：（1）晚泥盆-早石炭世（370-360 Ma）： 火山喷发时期，形成赋矿火山岩；（2）石炭纪（350-290 Ma）：矿床形成，并迅速遭受了沉积埋藏；（3）二叠纪（280-250 Ma）：继续沉积埋藏，吐拉苏盆地接受了大约 2.5 km 厚的沉积物，避免了浅成低温热液矿床的破坏；（4）渐新世以来快速剥露，大哈拉军山组火山岩之上的部分盖层被风化剥蚀，浅成低温热液矿床重新出露地表或近地表而被发现。综上， 提出京希-伊尔曼得金矿属高硫型浅成低温热液矿床。金来自于大哈拉军山组赋矿围岩，深源岩浆热液同样为矿床的形成提供了一定的成矿物质。 水岩作用引起的 pH 和氧逸度的变化是金沉淀的主要原因。 周期性的镁铁质岩浆补给维持了长期的热异常，并可能贡献了成矿金属和硫。成岩成矿作用发生在石炭纪。 成矿后的迅速沉积埋藏是矿床得以保存的重要因素。 |
| Other Abstract | Epithermal deposits are important sources of gold, copper, zinc and lead in theworld. About 12% of Au comes from this deposit. It is often characterized by largeserve, shallow burying and easy mining. Two types of high-sulfidation andlow-sulfidation have been distinguished, with the former has closely related to theporphyry deposits. Thus, it has been long hot spot in studies of deposits around theworld. Tulasu basin is located in the northern part of the Chinese western Tianshan,which is the largest epithermal gold deposits cluster in Xinjiang. Generally, theseepithermal deposits are mainly of low-sulfidation type. Jingxi-Yelmend deposit is theonly suspected high-sulfidation type, but was debated by absence of characteristicmineral. To settle such dispute, this study, detail field geological investigation,petrography, mineralogy, geochemistry and chronology studies were carried on, inorder to determine the mineralization accurately. The potential achievement cannotonly improve our understanding of metallogenetic regularity and preservation ofepithermal deposits in the Tulasu basin, but also is beneficial to the exploration andresource potential evolution in this area.Jingxi-Yelmend epithermal gold deposit is located in the northern margin ofTulasu basin. The bearing-ore strata are conglomerate member and acid tuff memberof the Dahalajunshan formation. The orebodies are mostly distribution in a carpet-likeand tapered. It is controlled by NW-, N-, E- and NE-trending faults. Wall alterationincludes strong silicification, argillic alteration and carbonation alteration. A largeamounts of marcasite (or coexist with pyrite) in the hydrothermal stage, indicatingthat the pH of ore-forming fluid was about 3 ~ 5 and oxidized, the temperature is<240 ℃. These features are in accordance with high-sulfidation epithermal deposit. Inaddition, the mineralization structure contains lots of acid leached porous quartz,which is commonly found in high-sulfidation epithermal deposit. In order to explore the mineralization process and mechanism of gold precipitation, detailed petrographicand mineralogical study are carried on the pyrite and marcasite, which are the maingold-bearing minerals. Jingxi-Yelmend deposit has undergone two stage ofmineralization, including sedimentary diagenesis and hydrothermal mineralization.Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS)microcell trace element analyses show that Au mainly existed in the form of invisiblegold (solid solution) in pyrite and marcasite. In the early sedimentary diagenetic stage,pyrite was mainly strawberry-shaped aggregates, while marcasite was characterizedby banding anhedral grains. The former contains Au (average of 12.0 ppm) and othertrace elements (Ti, Co, Ni, Cu, Zn, Ag, Sb and Pb), with Co/Ni value of 0.006 ~ 0.52,indicating the sedimentary environment. The latter Au and As was obvious depleted,while Al, Ti were enriched and Co, Ni, Cu, Zn, Pb were slightly depleted.Hydrothermal ore-forming stages further divided into: (1) the planar silicification -pyritization stage including three types of pyrite and two kinds of marcasite. Py1 wasporous anhedral-subhedral coarse grains. Py2 was euhedral-subhedral plate andfoliated fine grains. Py3 was disseminated flower-shape or euhedral fine grains, withobvious core-mantle-rim structure. Mrc1 is anhedral fine grains and intergrown withPy2. Mrc2 is fractured coarse grains. In this stage, the contents of Au in pyrite andmarcasite were very low. The average content of gold in Py1-Py3 were 0.001 ppm,0.001 ppm and 0.45 ppm, respectively, while the content of Mrc2 was < 0.01 ppm.Compared with Py0, the Co, Ni, Zn, Mo and Ag in pyrite and marcasite are relativelydepleted, while As, Cu, Sb, and Pb are enriched. (2) the hydrothermalbreccia-silicification stage has closed association with colloform pyrite and marcasite.Py4 was veinlet、 net vein or porous structure. Py5a was disseminated anhedralmicro-sized grains, BSE image showing obvious oscillatory zones. Py5b wasdisseminated irregular anhedral compact micro-sized grains. Mrc3 was spherical orgranular grains. Mrc4 was yellow-green anhedral grains and Mrc5 was brownanhedral grains. The content of Au in pyrite (Py4-Py5) and marcasite (Mrc3-Mrc5) were significantly increasing to 33.0 ppm, 1.2 ppm and 8.7 ppm, 0.05 ppm, 0.3 ppm,respectively. Other trace elements (Ag， Sb， Zn， Pb) are also significantly enriched inthis stage. (3) Quartz-carbonation stage was mainly consist of disseminatedeuhdedral-subhdedral compact Py6 and arsenopyrite. Au in Py6 is mostly lower thanthe detection limit. Compared with pyrite in other stages, the content of Au, As, Ti,Mo, Ag and Sb in Py6 is relatively low. Large number of colloidal pyrite andmarcasite indicate that the ore-forming hydrothermal fluids are low, and the suddenchange of physical and chemical conditions leads to the supersaturation ofore-forming hydrothermal fluids, thus causing Au precipitation.NanoSIMS in-situ sulfur isotope analysis of hydrothermal pyrite and marcasitefrom the Jingxi-Yelmend deposits provide important information for the source andevolution of ore-forming fluids. These pyrite and marcasite have δ34S values rangingfrom -35 ~ 11.5‰, but mainly fall into -10 ~ 10‰. The low δ34S values (-35 ~-22.9‰) of framboidal pyrite may represent the reduction of marine sulfate bybacteria in an open system. The δ34S values of pyrite and marcasite in the earlysilicification and pyritization stage were -13.6 ~ 9.3‰. This wide values of δ34Sindicates that sulfur comes from the sedimentary formation or fractional distillation.Heavy 34S enters the oxide, while the residual H2S is relatively poor 34S, resulting in alower value of δ34S in pyrite and marcasite. After magmatic hydrothermal activity,devulcanization and fluid interaction, sulfide produce negative δ34S values.Meanwhile, it was affected by the change of pH or oxygen of hydrothermal fluid. Inthe hydrothermal-brecciation stage, the δ34S values of pyrite and marcasite were -6.8~ 13.2‰, with mainly concentrated between -5 ~ 5‰, indicating that the sulfur wasdominated by magmatic sulfur.Accessory zircons were collected from the intermediate to felsic volcanic rocksoutcropped at the Jingxi-Yelmend gold deposit to constraint the link betweenvolcanism and mineralization. Detailed cathodoluminescence (CL) illustratesubiquitous resorption surfaces and embayments. According to the Zircon Ti thermometer, the zircon formation temperature in the sample is about 700 ~ 840 ℃. Insitu LA-ICPMS trace element analysis support periodic recharge of magma chamberby mafic magma input from depths. The youngest zircon grains (or sharp tips/rims)constraint two main pulses of magmatism at ~370 Ma and 365–362 Ma, respectively,although the longevity of a mobile magma chamber is estimated to 44–61 Ma, usingthe U-Pb age of the oldest zircon antecryst (406.9 5.4 Ma) and the youngest zircon(354.6 3.0 Ma) as cutting edge and taking the analytical uncertainty intoconsideration. Single grain (U-Th)/He dating of zircon from the first pulse yieldsnearly an age of 354 15 Ma, which is identical to U-Pb age within analyticaluncertainty. However, zircons from the second pulse of volcanic yield much younger(U-Th)/He centered at 292.6 7.6 Ma, indicating an unusually long thermal history.Further trace element analysis of zircon LA-ICP-MS indicates that deep magmasperiodically replenish the ore-forming magma chamber. Combined with previousstudies, we believe that the Jingxi-Yelmend deposit experienced five stage asfollowing: (1) Late Devonian-Early Carboniferous (370-360 Ma), a series of volcanicrocks formed, which were the main host rocks; (2) Carboniferous (350-290 Ma) forsedimentary burial and the gold deposits forming; (3) Permian (280-250 Ma) continuesedimentary and buried. Tulasu Basin received about 2.5 km of sediments, avoidingthe destruction of epithermal deposits; (4) Since the Oligocene, some of the coverlayers above the volcanic rocks of the Dahalajunshan formation have been eroded byweathering, and the epithermal deposits have reemerged or been discovered near thesurface.In conclusion, we propose Jingxi-Yelmend gold deposit is a high-sulfidationepithermal deposit. The gold comes from the host rocks of the Dahalajunshanformation, and the rising deep-source magmatic hydrothermal fluid. The change ofpH and oxygen fugacity caused by water-rock action is the main reason of goldprecipitation. Periodic replenishment of mafic magma controls the duration of fluid,metal, and sulfur release, as well as the duration of magmatic activity. Diagenesis and mineralization occurred in Carboniferous and rapid deposition after mineralization isan important factor for the preservation of epithermal deposits. |
| Subject Area | 地球探测与信息技术 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/15464 |
| Collection | 中国科学院新疆生态与地理研究所 研究系统 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 叶甜. 吐拉苏盆地高硫型浅成低温热液成矿系统的形成与保存[D]. 北京. 中国科学院大学,2020. |
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