Geochemical signature of porphyries in the Baogutu porphyry copper belt, western Junggar, NW China

The Baogutu porphyry copper belt lies in the Darbut transitional island arc of the western Junggar, in the western section of the Central Asian Orogenic Belt in NW China. Our new petrographic results for the ore-bearing porphyry stocks in the Baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified. The copper mineralization is hosted in the diorite, diorite porphyries and related breccias of the diorite porphyry stocks.Geochemical data indicate that the ore-bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc-alkaline, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Nb anomaly. REE patterns show distinct enrichments in LREE relative to HREE. The rocks also exhibit high initial εNd(t) (+ 2.7 to + 6.3) ratios and low initial ⁸⁷Sr/⁸⁶Sr values (0.70359–0.70397). Many samples are chemically similar to adakites (e. g. Yb < 1.9 ppm, Y < 18 ppm, Sr/Yb > 20, ⁸⁷Sr/⁸⁶Sr < 0.7045). These data are consistent with a transitional island arc from immature arc to mature arc and suggest that the ore-bearing porphyry system was derived from the partial melting of multiple sources including oceanic crust and a subduction-modified mantle wedge, with melts undergoing significant crystal fractionation during convergence between the paleo-Junggar ocean and the Darbut arc.     

Petrogenesis and tectonic settings of the Late Carboniferous Jiamantieliek and Baogutu ore-bearing porphyry intrusions in the southern West Junggar,NW China

Porphyry Cu deposits occurred in the southern West Junggar of Xinjiang, NW China and are represented by the Baogutu and newly-discovered Jiamantieliek porphyry Cu deposits. Petrographical and geochemical studies show that both Jiamantieliek and Baogutu ore-bearing intrusions comprise main-stage diorite stock and minor late-stage diorite porphyry dikes and are the calc-alkaline intermediate intrusions. Based on U–Pb zircon SHRIMP analyses, the Jiamantieliek intrusion formed in 313 ± 4 Ma and 310 ± 5 Ma, while, based on U–Pb zircon SIMS analyses, the Baogutu intrusion formed in 313 ± 2 Ma and 312 ± 2 Ma. Rocks in the Jiamantieliek intrusion are enriched in light rare earth elements (LREE) and large ion lithophile elements (LILE) with negative Nb anomaly. Their isotopic compositions (ε_Nd(t) = +1.6 to +3.4, (⁸⁷Sr/⁸⁶Sr)_i = 0.70369–0.70401, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.31–5.41) suggest a mixing origin from depleted to enriched mantle sources. In the Baogutu intrusion, the rocks are similar to those of the Jiamantieliek intrusion. Their Sr-Nd-Pb isotopic composition (ε_Nd(t) = +4.4 to +6.0, (⁸⁷Sr/⁸⁶Sr)_i = 0.70368–0.70385, (²⁰⁷Pb/²⁰⁴Pb)_i = 15.34–5.42) shows a more depleted mantle source. These features suggest generation in an island arc. The Jiamantieliek and Baogutu intrusions have similar characteristics, indicating that a relatively uniform and integrated source region has existed in the southern West Junggar since the Palaeozoic. A larger contribution of calc-alkaline magma would be required to generate the Jiamantieliek intrusion, which may reflect the development of magma arc maturation towards the western section of the southern West Junggar.     

Native antimony in the Baogutu gold deposit (west Junggar,NW China): Its occurrence and origin

The Baogutu gold deposit, West Junggar (Xinjiang, NW China), is composed of quartz–sulfide veins and their stockworks and is hosted within an Early Carboniferous volcanic–sedimentary sequence. Three ore-forming paragenetic stages can be identified: coarse-grained quartz–sulfide vein (stage I), gold-bearing fine-grained quartz–sulfide vein (stage II), and native antimony-bearing calcite–sulfide veinlets (stage III). The estimated formation temperatures (approximately 360 to 220 °C), fS₂ (? 7 to ? 15 log units), and fO₂ (? 26 to ? 43 log units) decrease from stage I, through stage II, to stage III. The nature of the hydrothermal fluid changed from weakly acidic (pH: 5 to 6 at stage I) to alkaline (pH: > 7 at stage III).Two different occurrences of native antimony could be identified: one coexists with chalcopyrite and pyrrhotite, whereas the other occurs as isolate grains within calcite veins. Native antimony (up to 100 μm in size) contains minor amounts of As (2.0 to 2.7 wt.%); empirical formula Sb_0.95–0.96As_0.03–0.04. Decrease of temperature and fO₂ at high pH and low fS₂ conditions favored co-precipitation of native antimony–ullmannite assemblages and the decomposition of tetrahedrite. Native antimony crystallized later than the native gold, suggesting fractionation between Au and Sb during the hydrothermal evolution of the deposit.     

新疆西准噶尔包古图中酸性岩体氟地球化学研究

氟是岩浆-热液作用过程中常见的矿化剂元素,对成矿过程的理解至关重要。新疆西准噶尔包古图地区产出斑岩型铜矿床,Ⅰ、Ⅱ、Ⅲ-1号岩体矿化程度差,金属矿物体积分数1%,表现为浸染状分布的黄铜矿、黄铁矿和磁黄铁矿;Ⅲ-2号岩体矿化中等,金属矿物体积分数1%~5%,主要为黄铜矿、黄铁矿和磁黄铁矿,少量毒砂、辉钼矿、斑铜矿、黝铜矿、闪锌矿和银金矿。V号岩体产出大型斑岩铜矿床,矿石样品金属矿物体积分数15%,浸染状和硫化物脉体常见。样品氟含量测试结果显示,弱矿化花岗闪长岩的氟含量为(300~512)×10~(-6),平均为394×10~(-6),中等矿化花岗闪长岩和石英闪长岩的氟含量为(287~573)×10~(-6),平均为427×10~(-6),斑岩铜矿矿石样品的氟含量为(466~811)×10~(-6),平均为639×10~(-6),明显高于弱矿化和中等矿化样品。随氟含量升高,样品的铜含量逐渐升高,指示氟对铜在流体中的迁移有利。     

西准噶尔包古图I号岩体的锆石U-Pb年代学和地球化学特征

西准噶尔包古图地区发育一些小型的闪长质岩体。前人对这些小岩体开展了岩石学、年代学和地球化学等研究,然而,其成因机制和构造背景仍然存在争议,阻碍了区域构造演化和成矿作用的认识。本文在前人研究的基础上,选择包古图I号岩体为研究对象,有望揭示包古图岩体的岩石成因和构造背景。锆石U-Pb年代学研究显示,包古图I号岩体形成于（313.8±1.1）Ma。包古图I号闪长岩体以富SiO₂（58.0%~59.0%）、Al₂O₃（16.6%~17.4%）和Sr（757×10^-6~882×10^-6）,低的Y（14.6×10^-6~15.7×10^-6）和Yb（1.51×0^-6~1.60×0^-6）质量分数为特征,具有高的Sr/Y（50~59）值和弱的Eu异常,类似于俯冲成因的埃达克岩。另外,这些闪长岩具有较高的Mg（w（MgO）=3.46%~3.77%,Mg^#=52.8~53.2）,高的Cr（63.8×10^-6~74.7×10^-6）和Ni（45.2×10^-6~49.8×10^-6）质量分数,亏损HFSE（Nb,Ta和Ti）。该闪长质岩体可能由俯冲的板片熔体与上覆地幔相互作用而成。它的形成可能与西准噶尔地区晚石炭世的洋脊俯冲作用有关。     

西准噶尔灰绿山西三岔沟金矿点的发现及地质意义

在新疆西准噶尔灰绿山西开展的地球化学剖面上,发现三岔沟金矿点。通过填图、钻探、槽探揭露,发现矿体随脉岩断续产出,品位0.10～13.1 g/t,深部延伸稳定。金矿石组合为黄铁矿、针铁矿、赤铁矿、磁铁矿、褐铁矿、自然金等中低温热液型矿石组合特征。金以自然金、碳酸盐包裹金、硫化物包裹金3种方式存在。将之与邻区金矿成矿特点进行对比,矿体产于泥盆系中酸性脉岩之中,具构造控矿和脉岩控矿双重控矿性。     

Millerite-Maucherite-Pentlandite-Heazlewoodite in the Sartohay Chromite Deposit, West Junggar, Xinjiang, China

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Geological Evolution and Related Gold Deposits in West Junggar, Xinjiang, China

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Collective Prospecting Indicator of the Mudanjiangwulin Town Intrusion-related Gold Deposit in Heilongjiang Province

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西准噶尔构造带包古图组的岩石组合及其时限

包古图组是新疆西准噶尔增生造山带西北缘石炭纪密西西比亚纪重要沉积记录。确认其完整的沉积序列、岩石组合及其与上覆和下伏地层的接触关系,对解析本区晚古生代盆地构造演化具有重要意义。本文新实测的白碱滩北红山梁剖面上,出露了岩石组合截然有别,色调区分性极强的两大套地层,上部深灰—灰黑色调“（含碳）细碎屑岩”与其下伏鲜红色调的“硅质岩- 凝灰质硅质粉砂岩间夹中基性火山岩”为连续沉积（整合接触）,分属包古图组和红山梁组。本文于包古图组底部和红山梁组顶部分别获得345. 1 Ma和365. 9 Ma的LA- ICP- MS锆石U- Pb年龄,限定其时代分别为密西西比亚纪和晚泥盆世。这一新发现,不仅确立了包古图组是区内石炭纪最老地层单位,佐证了包古图组老于希贝库拉斯组这一久争悬疑,而且使得区内密西西比亚系有了完整的地层序列,揭秘了石炭系最底部的沉积建造及其岩石组合,也为完整认识泥盆纪—石炭纪这一重要时期的盆地沉积特征及其构造演化提供了新资料。     

西准噶尔哈图金矿床后期变化研究

研究发现后期岩浆热液作用是造成哈图金矿床两类金矿体之一的石英脉型矿体的产生,构造活动对金矿体后期变化的影响较小,含矿石英脉上部因风化剥蚀作用消火,勘查中需要考虑矿床后期变化因素.     

Puziwan Gold Deposit in Shanxi, China: A Special Linear Cryptoexplosive Breccia Type Gold Deposit

The Puziwan gold deposit is a special linear cryptoexplosive breccia type deposit found in northeastern Shanxi, China, in recent years. The deposit is located in a secondary metallogenic. belt of the most famous Au-Ag polymetallic metallogenic belt along the north margin of the North China platform. The secondary metallogenic belt is a synmagmatic tension-shear fault-fracture belt of ENE linear trend. The Indosinian cryptoexplosive breccia body, quartz monzonitic porphyry (beschtauite breccia), quartz monzonite (243.7 Ma, K-Ar), Yanshanian granite-porphyry (105±6 Ma, Rb-Sr) and orebodies mostly occur as dykes or veins and short lenses along the structural fracture belt. The orebodies are emplaced in the fractured cryptoexplosive breccia body in the tectonomagmatic belt and their attitude is consistent with that of the breccia body. The orebodies have two types: one is shallow-seated thick and big ones, which are short-lenticular in plan and wedge-shaped in cross section, shallow buried, large in size a     

新疆西准噶尔包古图地区中酸性侵入体的岩石学、年代学和地球化学研究

新疆西准噶尔包古图地区出露一些中酸性小岩体,以花岗闪长岩、石英闪长岩和闪长岩为主,富Na贫K,属于亚碱性岩石,Mg#值较高(平均0.48)。锆石U-Pb年代学研究表明其形成于310~319Ma期间。通过对比研究,划分出两种侵入体类型:I、Ⅱ、Ⅴ号岩体属于磁铁矿型侵入体,具有较高的氧逸度特征(LogfO2=-22~-16);Ⅲ号岩体属于钛铁矿型侵入体,显示较低的氧逸度特征。这些侵入体具有相似的微量元素和同位素地球化学特征:富集Cs、Rb、Ba、Th、U和LREE,亏损Nb、Ta、Ti,无明显Eu异常;(87Sr/86Sr)i为0.7036~0.7038,εNd(t)为6.64~8.30;具有年轻的Nd模式年龄tDM1=435.4~587.7Ma。元素和同位素地球化学特征显示,包古图中酸性侵入体是受交代的亏损地幔部分熔融生成的玄武质岩浆经历高度结晶分异之后的产物(可能发生岩浆混合),古老地壳物质的混染很弱。     

Early Carboniferous intra-oceanic arc and back-arc basin system in the West Junggar,NW China

A series of Lower Carboniferous volcanic rocks occur in the Hatu, Darbut, and Baogutu areas of Xinjiang Province. Secondary ion mass spectrometry (SIMS) zircon U–Pb isotopic data indicate that two samples of these rocks coevally erupted at 324.0 ± 2.8 Ma and 324.9 ± 3.4 Ma. Three detailed profile measurements show that the volcanics include the Hatu basalt, the Baogutu andesite and dacite, and the Darbut andesite. Whole-rock compositions suggest that the Hatu volcanics are tholeiites and have a mid-ocean ridge basalt (MORB)-like signature with a small negative Nb anomaly, suggesting formation in a back-arc basin. Their isotopic compositions (?Nd(t) = +2.2 to +4.0, (⁸⁷Sr/⁸⁶Sr)i = 0.70414 to 0.70517) suggest a mixing origin from depleted to enriched mantle sources. In contrast, the Baogutu and Darbut rocks are andesite and dacite possessing a transitional tholeiite to calc–alkaline character and have E-MORB-like and OIB signatures, with a marked negative Nb anomaly and Th/Yb-enrichment, indicating that they were generated in a subduction zone setting. Isotopically, they display consistently depleted Sr–Nd isotopic compositions [(⁸⁷Sr/⁸⁶Sr)i = 0.70377–0.70469, ?Nd(t) = 1.0–5.2], suggesting that they were derived from a depleted mantle, and that fluid and sediments were involved in their petrogenesis. These features suggest that an early Carboniferous intra-oceanic arc and back-arc basin system generated the studied volcanic units in the West Junggar.     

西准噶尔宝贝金矿地质与容矿火山岩的锆石SHRIMP年龄

位于西准噶尔的宝贝金矿主要由石英脉型矿石组成,主要含金矿物为银金矿,以裂隙金和包裹金的形式赋存在毒砂、黄铁矿和石英中。宝贝金矿的黄铁矿普遍含As（最高达3.88%,平均1.49%）。根据脉穿切和矿物共生组合可将宝贝金矿的成矿作用划分出四个成矿阶段：钠长石–石英阶段（I）、银金矿–黄铁矿–毒砂–石英阶段（II）、多金属硫化物浸染状矿化阶段（III）和碳酸盐化阶段（IV）,其中第II和III阶段为主要成矿期。利用锆石SHRIMP方法测定了赋矿围岩（酸性凝灰岩）的形成时代,其U–Pb谐和年龄为328.1±1.8 Ma（MSWD＝1.6, n＝13）。该年龄代表宝贝金矿赋矿围岩的形成时间,即西准噶尔地区大规模中酸性火山岩的喷发时间。     

新疆包古图斑岩铜矿矿床地质特征

新发现的包古图斑岩铜矿床位于准噶尔盆地西缘,达尔布特断裂以南的包古图地区。通过对 V 号主要赋矿岩体及钻孔岩心的野外和镜下观察,研究了矿体矿化情况、蚀变分带特征和矿石组合。对该矿床的流体包裹体分类研究表明,主成矿期成矿温度在180℃～450℃,包裹体的形成压力多在1～9MPa。由此得出的斑岩体的侵位深度在100～600m。黄铜矿和黄铁矿的δ~(34)S 变化范围分别是-2.4‰～-0.8‰和-2.7‰～ 0.7‰。对该矿床的初步研究认为,矿床是在埃达克质岩浆侵位到地壳浅部冷却成岩后,经历了两期含矿热液的作用而成矿的。早期形成 Cu、Fe、Mo、Zn 的硫化物矿物,可划分为4个成矿阶段;晚期形成 Cu-Te-Bi-Au-Ag 的复杂矿物组合。早期矿化形成的辉钼矿 Re-Os 年龄是310Ma。     

Geology of Qiaoxiahala Fe-Cu-Au Deposit: A Paleozoic IOCG Deposit in Altaids, NW China

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新疆吐克吐克铜矿黄铜矿Re-Os定年及成矿意义

吐克吐克铜矿为笔者新发现,产于新疆西准噶尔构造带南部,成矿时代尚缺乏精确的同位素年代学制约。该矿床硫化物组合单一,主要为黄铜矿。本文选择了8件黄铜矿样品,进行Re-Os法定年。结果得到了较好的效果,所有样品的Re含量为39.7×10~(-12)~2440.6×10~(-12),~(187)Os含量为1.2×10~(-12)~9.0×10~(-12),给出的等时线年龄为288.3±8.8Ma。这表明该区Cu的成矿作用与晚石炭世—早二叠世区域峰期岩浆活动一致,证实该区仍存在较大找矿空间。