Genesis of the Kamioka Skarn Deposits: An Important Role of Clinopyroxene Skarn and Graphite-bearing Limestone in Precipitating Sulfide Ore

Abstract: A genetical relationship between skarn formation and mineralization is investigated for the Kamioka skarn deposits which are the largest Zn-Pb producer in Japan. In the Mozumi deposit, one of main deposits in the Kamioka mining area as well as Tochibora and Maruyama, clinopyroxene skarn was generally subjected to later replacement by garnet or magnetite–calcite–quartz during the Zn-Pb mineralization. The replacement of hedenbergitic clinopyroxene by andraditic garnet resulted in the formation of diopsidic clinopyroxene relicts. With the progress of replacement, the S/So value (So: an estimated area occupied by an original clinopyroxene grain in a thin section, S: a total area of relict clinopyroxene fragments) which is an index of the degree of replacement decreases from 0. 7 to 0. 1, and the hedenbergite mole percent of relict clinopyroxene decreases drastically from about 65 to less than 40. A close association of andraditic garnet and sphalerite suggests that heden-bergitic clinopyroxene skarn played an important role to reduce the relatively oxic ore-forming fluid enriched in Zn²⁺ and SO4^2– and to precipitate sphalerite from the fluid. Ferrous iron in the hedenbergitic clinopyroxene skarn was oxidized to form andraditic garnet. Besides this garnet formation, the mineral assemblage of magnetite–calcite–quartz replaced the clinopyroxene skarn at the time of mineralization. In both cases, the reduction of relatively oxic ore-forming fluid by hedenbergitic clinopy-roxene skarn at the later stage brought about the precipitation of sulfide minerals. In contrast, these types of later replacement are not found in the Tochibora deposit. Instead, graphite-bearing crystalline limestone and relatively fresh clinopyroxene skarn are common. Mineralized clinopyroxene skarn has high graphite carbon contents relative to barren one, suggesting that the amount of graphite in the skarn was an important controlling factor for mineralization. It is very likely that the graphite played a role of reducing agent during the mineralization in the Tochibora deposit.     

Hydrothermal Alteration of Limestone and Mineral Exploration of Zn-Pb Skarn Deposits in the Sako-nishi Area of the Kamioka Mine, Central Japan

Abstract: Crystalline limestone of the Sako-nishi area in the Kamioka Zn-Pb mine, central Japan, is depleted in ¹⁸O and ¹³C toward the center of mineralization due to interaction with hydrothermal fluids with a dominant meteoric water component. The relationship between isotopic composition and mineral assemblage, texture, the chemical composition of the minerals, and the bulk chemical composition in the limestone was examined. A decrease in the δ¹⁸OSMOW value correlated with: (1) increase of fine-grained calcite which is enriched in Mn and exhibits a bright cathodoluminescence, (2) progressive hy-drothermal alteration of clinopyroxene in the original limestone into tremolite within the weakly-altered zone, and into chlorite and actinolite within the strongly-altered zone, (3) dominance of hydrothermal chlorite in altered limestone having δ¹⁸O values of less than 10%. This chlorite was enriched in Fe compared to mafic minerals in the unaltered limestone. The enrichment of Fe and Mn was more conspicuous in calcite and chlorite in skarn deposits. The occurrence and chemical composition of hydrothermal minerals in the limestone, skarn, and ore indicate that the ¹⁸O–depleted zones were formed in the later stage from fluids, which were responsible for mineralization and skarnization, and for Fe and Mn enrichment. The Al, Mn, and Fe contents, and the ratios of Mg/(Mg+Mn+Fe), Al/Mg, and Mn/Sr in the hydrochloric acid leachate of limestone varied with decreasing δ¹⁸O and δ¹³C values, reflecting increases in high-Mn calcite and high-Fe chlorite. These indexes were useful for the identification of hydrothermally altered limestone. Furthermore, the potential score weighted by each index was more effective and accurate means of detecting promising mineralization zones. An anomalous potential score due to the presence of hydrothermal minerals in the outcropping limestone occurred along the Atotsu–1GO fault. This structure indicates that the skarn deposits of the Sako-nishi area belong to Mozumi-type Zn–Pb skarn deposits, in which fissures and faults served as major passages for the hydrothermal fluid. High-Mn carbonate and high-Fe chlorite widely occur in base-metal vein deposits and Zn-Pb type skarn deposits. Leaching of altered rock with hydrochloric acid in addition to stable isotope composition and cathodoluminescence imaging is effective for geochemical exploration for hydrothermal deposits because it makes possible the detection of the elemental composition of hydrothermal minerals such as chlorite and carbonate and because of the rapidity and convenience of analysis.     

Geochemistry and Genesis of Iron-apatite Ore in the Khanlogh Deposit, Eastern Cenozoic Quchan-Sabzevar Magmatic Arc, NE Iran

The Khanlogh deposit in the Cenozoic Quchan-Sabzevar magmatic belt, NE Iran, is hosted by Oligocene granodioritic rock. The Khanlogh intrusive body is I-type granitoid of the calc-alkaline series. The orebodies are vein, veinlet, massive, and breccia in shape and occur along the fault zones and fractures within the host rock. Ore minerals dominantly comprise magnetite and apatite associated with epidote, clinopyroxene, calcite, quartz, and chlorite. Apatites of the Khanlogh deposit have a high concentration of REE, and show a strong LREE/HREE ratio with a pronounced negative Eu anomaly. Magnetites have a high concentration of REE and show weak to moderate LREE/HREE fractionation. They are comparable to the REE patterns in Kiruna-type iron ores and show an affinity to calc-alkaline magmas. The Khanlogh deposit is similar in the aspects of host rock lithology, alteration, mineralogy, and mineral chemistry to the Kiruna-type deposits. Field observations, hydrothermal alteration halos, style of mineralization, and the geochemical characteristics of apatite, magnetite, and host rock indicate that these magnetite veins have hydrothermal origin similar to Cenozoic Kiruna-type deposits within the Tarom subzone, NW Iran, and are not related to silica-iron oxide immiscibility, as are the major Precambrian magnetite deposits in central Iran.     

桓仁夕卡岩型多金属矿床地质特征与流体包裹体研究

桓仁夕卡岩型多金属矿床位于辽东裂谷北部边缘与太子河凹陷复合部位, 产于燕山晚期侵入闪长 杂岩与寒武纪沉积灰岩接触带间的夕卡岩内。夕卡岩矿物可以分为进变质阶段蚀变矿物组合和退变质阶段 蚀变矿物组合, 成矿元素由深部向浅部具有Fe→Cu（Mo）→Zn→Pb 的转换规律, 具有明显的分带分段性。为 了探讨成矿流体的物理化学性质及其演化史, 选择了石榴子石和方解石中的气液两相流体包裹体进行研究。 数据测试表明, 石榴子中流体包裹体的均一温度范围为376.1~450.0 ℃, 平均411.6 ℃; 方解石中流体包裹 体的均一温度范围为122.6~170.0 ℃和178.3~270.2 ℃, 平均值分别为149.5 ℃和204.5 ℃, 冰点温度范围 为？4.2 ~ ？17.6 ℃, 与前人研究成果相吻合, 与国内外其他夕卡岩矿床相比, 数据具有实际和理论研究意义。 本矿床Fe-Cu（Mo）、Cu-Zn、Zn-Pb 矿体的形成温度分别集中于约410 ℃、400~300 ℃、约150 ℃和约200 ℃。 以往Pb、S 和D-O 地球化学数据和本次研究REE 特征显示, 岩浆流体起源于上地幔, 在上升过程中携带了 大量成矿物质, 在进变质阶段和退变质阶段, 成矿流体交代形成特定的夕卡岩矿物组合, 退变质阶段的后期 阶段, 有了大气降水的参与, 单一来源的岩浆流体转化为了混合流体。     

Garnetization as a ground preparation process for copper mineralization: evidence from the Mazraeh skarn deposit, Iran

The Mazraeh Cu–Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene–Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced Si, Fe, Mn, Ca, Mg, P, Ag, Cu, Zn, La, Pb, Cd, Mo, and Y. The main mass loss in the garnet skarn was due to destruction of feldspars in the Mazraeh plutonic rocks and leaching of K₂O and Na₂O. Released Ca has been fixed in the andraditic garnet. Garnetization of the Mazraeh pluton was accompanied by mass and volume increase. The magnitude of these changes depends mainly on the degree of alteration and composition of the precursor. The brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured. These fractures not only facilitated movement of hydrothermal fluids but also provided new locations for Cu mineralization. Therefore locating strongly garnetized zones may be a vector to ore in skarn deposits.     

The origin and evolution of skarn-forming fluids from the Phu Lon deposit,northern Loei Fold Belt,Thailand: Evidence from fluid inclusion and sulfur isotope studies

The Phu Lon skarn Cu–Au deposit is located in the northern Loei Fold Belt (LFB), Thailand. It is hosted by Devonian volcano-sedimentary sequences intercalated with limestone and marble units, intruded by diorite and quartz monzonite porphyries. Phu Lon is a calcic skarn with both endoskarn and exoskarn facies. In both skarn facies, andradite and diopside comprise the main prograde skarn minerals, whereas epidote, chlorite, tremolite, actinolite and calcite are the principal retrograde skarn minerals.Four types of fluid inclusions in garnet were distinguished: (1) liquid-rich inclusions; (2) daughter mineral-bearing inclusions; (3) salt-saturated inclusions; and (4) vapor-rich inclusions. Epidote contains only one type of fluid inclusion: liquid-rich inclusions. Fluid inclusions associated with garnet (prograde skarn stage) display high homogenization temperatures and moderate salinities (421.6–468.5 °C; 17.4–23.1 wt% NaCl equiv.). By contrast, fluid inclusions associated with epidote (retrograde skarn stage) record lower homogenization temperatures and salinities (350.9–399.8 °C; 0.5–8 wt% NaCl equiv.). These data suggest a possible mixing of saline magmatic fluids with external, dilute fluid sources (e.g., meteoric fluids), as the system cooled. Some fluid inclusions in garnet contain hematite daughters, suggesting an oxidizing magmatic environment. Sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of δ³⁴S values (?2.6 to ?1.1 ‰ δ³⁴S), suggesting that the ore-forming fluid contained sulfur of orthomagmatic origin. Overall, the Phu Lon deposit is interpreted as an oxidized Cu–Au skarn based on the mineralogy and fluid inclusion characteristics.     

新疆西天山查岗诺尔铁矿床磁铁矿和石榴石微量元素特征及其对矿床成因的制约

查岗诺尔大型磁铁矿床位于西天山阿吾拉勒东段,赋存于下石炭统大哈拉军山组安山岩及安山质火山碎屑岩之中,主体矿底板夹透镜状的大理岩,矿体主要为层状、似层状、透镜状。根据矿石组构和矿物共生特征,可以划分为岩浆期和热液期两个成矿期,后者包括矽卡岩和石英-硫化物两个亚成矿期,进一步可以细分为6个成矿阶段。岩浆期的磁铁矿∑REE很低,稀土配分模式大致呈轻稀土、重稀土较富集而中稀土亏损的U型,富Ti、V、Cr,表明铁质可能来自安山质岩浆的结晶分异作用; 矽卡岩亚成矿期的磁铁矿∑REE极低,略微富集LREE,其它稀土元素亏损强烈,贫Ti、V,略富集Ni、Co和Cu。矽卡岩亚期的含矿和无矿矽卡岩中的石榴石的稀土配分模式类似,∑REE含量相对较高,呈HREE富集、LREE亏损、弱正Eu异常的分布型式,显示了交代成因石榴石的特征,暗示与其共生的磁铁矿也是通过热液流体与围岩地层的交代反应生成的,铁质来自围岩。结合矿床地质与微量元素地球化学,认为查岗诺尔铁矿可能是岩浆型和矽卡岩型(主要)的复合叠加矿床。     

层控夕卡岩及有关矿床形成过程的稀土元素行为——以安徽冬瓜山矿床为例

对安徽省冬瓜山层控夕卡岩型铜（金）矿床中穿层方向上不同蚀变程度的大理岩，顺层方向上距岩体远近不同但垂向深度的块状石榴子石夕卡岩及其主矿物石榴子石，不同演化阶段的石英及矿石等到的REE特征进行了系统研究，结果显示，在穿层方向上，大理岩被交代的程度愈深其稀土总量（∑REE）愈高，Eu负异常愈显著，尽管，夕卡岩全岩的RE分布模式与原岩（大理岩）相似，但前者的稀土总量（∑REE）远高于后者，且Eu异常更为显著，显然不是继续承原岩的REE特征所致，而是受控于其主矿物石榴子石的REE特征，后者又由参与交代作用的岩浆热液REE所决定，热液中的REE具有缓和右倾型分布模式，LREE富集，较显著的Eu负异常等基本特征，石榴子石晶体基本承袭了热液的REE特征，REE的空间变化特征结果地层的构造特征可以揭示夕卡岩及相关矿体形成过程中流体的输运径及输运方式，REE的研究有助于深化对层控夕卡岩及其相关矿床形成过程的认识。     

Genesis for Rare Earth Elements Enrichment in the Permian Manganese Deposits in Zunyi,Guizhou Province,SW China

The Zunyi manganese deposits, which formed during the Middle to Late Permian period and are located in northern Guizhou and adjacent areas, are the core area of a series of large-medium scale manganese enrichment minerogenesis in the southern margin and interior of the Yangtze platform, Southern China. This study reports the universal enrichment of rare earth elements(REEs) in Zunyi manganese deposits and examines the enrichment characteristics, metallogenic environment and genesis of REEs. The manganese ore bodies present stratiform or stratoid in shape, hosted in the silicon–mud–limestones of the Late Permian Maokou Formation. The manganese ores generally present lamellar, massive, banded and brecciated structures, and mainly consist of rhodochrosite, ropperite, tetalite, capillitite, as well as contains paragenetic gangue minerals including pyrite, chalcopyrite, rutile, barite, tuffaceous clay rock, etc. The manganese ores have higher ΣREE contents range from 158 to 1138.9 ppm(average 509.54 ppm). In addition, the ΣREE contents of tuffaceous clay rock in ore beds vary from 1032.2 to 1824.5 ppm(average 1396.42 ppm). The REEs from manganese deposits are characterized by La, Ce, Nd and Y enriched, and existing in the form of independent minerals(e.g., monazite and xenotime), indicating Zunyi manganese deposits enriched in light rare earth elements(LREE). The Ce_(anom) ratios(average-0.13) and lithofacies and paleogeography characteristics indicate that Zunyi manganese deposits were formed in a weak oxidation-reduction environment. The(La/Yb)_(ch), Y/Ho,(La/Nd)_N,(Dy/Yb)_N, Ce/Ce* and Eu/Eu* values of samples from the Zunyi manganese deposits are 5.53–56.92, 18–39, 1.42–3.15, 0.55–2.20, 0.21–1.76 and 0.48–0.86, respectively, indicating a hydrothermal origin for the manganese mineralization and REEs enrichment. The δ~(13) C_(V-PDB)(-0.54 to-18.1‰) and δ~(18) O_(SMOW)(21.6 to 26.0‰) characteristics of manganese ores reveal a mixed source of magmatic and organic matter. Moreover, the manganese ore, tuffaceous clay rock and Emeishan basalt have extremely similar REE fractionation characteristic, suggesting REEs enrichment and manganese mineralization have been mainly origin from hydrothermal fluids.     

新疆蒙库铁矿床稀土元素地球化学及对铁成矿作用的指示

新疆富蕴县蒙库大型铁矿呈层状、似层状、透镜状赋存于下泥盆统康布铁堡组变质火山-沉积岩系中.矿体中发育矽卡岩,但矽卡岩并不产在侵入岩接触带上.绿帘石、石榴石和矿石的稀土配分模式具有相似性,均为轻稀土富集,正铕异常,基本上无铈异常,暗示它们之间存在成因联系.石榴石稀土配分模式呈折线型,具有明显的正铕异常,石榴石流体包裹体中熔融包裹体、熔流包裹体和气液包裹体共存,表明石榴石矽卡岩具有岩浆成因和热液成因的特征,形成于晶体 熔体 流体三相共存的岩浆-热液过渡阶段.矿床地质特征、矽卡岩矿物和矿石稀土特征表明蒙库铁矿为矽卡岩型矿床.     

The composition of garnet in garnet-rich rocks in the southern Proterozoic Curnamona Province, Australia: an indicator of the premetamorphic physicochemical conditions of formation

Garnet-rich rocks occur throughout the Proterozoic southern Curnamona Province, Australia, where they are, in places, spatially related to Broken Hill-type Pb-Zn-Ag deposits. Fine-scale bedding in these rocks, their conformable relationship with enclosing metasedimentary rocks, and their enrichment in Mn and Fe suggest that they are metamorphosed chemical precipitates. They formed on the floor of a 1.69?Ga continental rift basin from hydrothermal fluids mixed with seawater and detritus. Garnet in garnet-quartz and garnet-amphibole rocks is generally light rare earth element (LREE) depleted, and has flat heavy REE (HREE) enriched chondrite-normalized REE patterns, and negative Eu anomalies (Eu/Eu*?<?1). Garnet in garnet-rich rocks from the giant Broken Hill deposit has similar REE patterns and either positive (Eu/Eu*?>?1) or negative Eu anomalies. Manganese- and Mn-Ca-rich, Fe-poor garnets in garnetite, garnet-hedenbergite, and garnet-cummingtonite rocks at Broken Hill have Eu/Eu*?>?1, whereas garnet in Mn-poor, Fe-rich quartz garnetite and quartz-garnet-gahnite rocks from Broken Hill, and quartz garnetite from other locations have Eu/Eu*?<?1. The REE patterns of garnet and its host rock and interelement correlations among REEs and major element contents in garnet and its host rock indicate that the Eu anomaly in garnet reflects that of its host rock and is related to the major element composition of garnet and its host rock. The value of Eu/Eu* in garnet is related to its Mn, Fe, and Ca content and that of its host rock, and the distribution of REEs among garnet and accessory phases (e.g., feldspar). Positive Eu anomalies reflect high amounts of Eu that was preferentially incorporated into Mn- and Mn-Ca-rich oxides and carbonates in the protolith. In contrast, Eu/Eu*?<?1 indicates the preferential discrimination against Eu by Fe-rich, Mn-poor precursor minerals. Precursors to Mn-rich garnets at Broken Hill formed by precipitation from cooler and more oxidized hydrothermal fluids compared to those that formed precursors to Mn-poor, Fe-rich garnet at Broken Hill and the other locations. Garnet from the Broken Hill deposit is enriched in Zn (> 400?ppm), Cr (> 140?ppm), and Eu (up to 6?ppm and positive Eu anomalies), and depleted in Co, Ti, and Y compared to garnet in garnet-rich rocks from other localities. These values, as well as MnO contents ?>?15 wt. % and Eu/Eu*?>?1 are only found at the Broken Hill deposit and are good indicators of the presence of Broken Hill-type mineralization.     

新疆霍什布拉克铅锌矿床微量元素地球化学

霍什布拉克铅锌矿床是新疆西南天山地区晚古生代碳酸盐岩容矿的重要矿床。本文采用高精度电感耦合等离子质谱(ICP-MS)对主要矿石矿物(黄铁矿、方铅矿、闪锌矿)和热液脉石矿物方解石进行了微量元素地球化学研究。研究表明,黄铁矿、方铅矿、闪锌矿、方解石具有较为相似的稀土元素特征,Eu正异常明显,弱负或弱正Ce异常指示成矿流体最初由相对氧化的条件演化为还原条件。与霍什布拉克岩体、容矿围岩的稀土元素组成进行对比后发现,硫化物及热液方解石稀土元素配分曲线部分与重结晶泥晶灰岩重合,结合前人同位素地球化学研究,认为容矿坦盖塔尔组碳酸盐岩为成矿提供了必要的成矿物质及成矿流体组分。Ga/In值显示闪锌矿为低温成矿;硫化物明显富集LREE,Hf/Sm、Nb/La和Th/La值小于1,显示铅锌成矿过程中成矿流体主体以富Cl为特征;Y/Ho、Zr/Hf和Nb/Ta值变化范围相对较小,表明成矿期流体性质相对较为稳定,基本未混入外来流体。     

Oxygen isotope study of the Kamioka Zn-Pb skarn deposits,Central Japan

The Kamioka Zn-Pb deposits consist of clinopyroxene-rich skarns replacing limestone lenses in Hida gneissose rocks. Paleozoic metabasite, early Jurassic Funatsu granitic rocks and late Cretaceous porphyritic dikes and stocks, are the known igneous rocks in the mining area. Oxygen isotopic compositions of eight separates each of clinopyroxene and quartz from the deposits (Table 1), and some minerals and rocks from the major rock units around the deposits (Table 2), have been analyzed. The estimated oxygen isotopic ratios of the fluids responsible for the formation of the deposits, range as low as -4 to +3 (SMOW). These values are considerably lower than expected from magmatic waters, and demonstrate that none of the igneous rocks in the area could be a direct source of the skarn- and ore-forming fluids. The data instead show that the deposits are formed by a huge convective circulation of solutions of meteoric water origin, promoted by a hidden batholithic intrusion at the time of the late Cretaceous.     

东蒙地区夕卡岩石榴石稀土元素地球化学及其成因

东蒙地区为我国北方重要的夕卡岩型锡银铜铅锌多金属成矿区，不仅矿床发育，而且成矿种类较多，典型矿床有黄岗梁Fe（Sn）、白音诺Pb-Zn-Ag等金属和浩布高Fe（Sn）－PbZnAg（Cu）矿床。研究表明，它们都是中生代岩浆岩与本区二叠系地层相互作用的产物。本文通过对黄岗梁、白音诺和浩布高3个矿床中不同阶段的石榴石夕卡岩矿物学研究，划分出早晚两期夕卡岩石榴石矿物。早期以浅色、他形细粒、均质的钙铁榴石为主，多形成环带的核心；晚期以深色、半自形中粗粒、弱非均质的钙铝榴石为主，多构成环带的边部。同时采用ICP－MS方法对3其中石榴石比较发育的黄岗梁和浩布高2个矿床中石榴石单矿物进行了稀土元素含量的测定。结果表明，矿区早期的石榴石具有岩浆成因的特征，晚期石榴石具有热液交代成因特征，即东蒙地区既有早期岩浆阶段的岩浆型夕卡岩，又有晚期热液交代型夕卡岩的多成因认识。     

新疆阿尔泰吉伯特铁矿床包裹体特征研究

吉伯特铁矿是新疆阿勒泰地区产于泥盆纪海相火山岩中的小型矿床。本文对吉伯特铁矿床的包裹体开展了研究,识别了熔体包裹体、熔体-流体包裹体以及富晶体的流体包裹体,并对其进行了初步的显微测温、激光拉曼光谱和电子探针等研究。熔体包裹体中含有富Si玻璃质、贫Si富Fe熔体、石英、萤石、方解石、磁铁矿等多种成分,它们分别组成不同的包裹体组合。熔体包裹体、熔体-流体包裹体和流体包裹体的存在表明它们被捕获时是一种熔体与流体共存的不混溶状态,这充分说明了吉伯特铁矿床的形成与岩浆熔体、岩浆-热液过渡性流体有直接的成因联系。吉伯特铁矿床中Fe的矿化是一个熔体相逐渐减少,流体相逐渐增加的连续演化过程,它受岩浆作用、岩浆-热液过渡性流体以及矽卡岩作用的共同制约。     

矿物——成矿与找矿

单颗粒矿物微量元素激光原位定量分析测试数据的大量积累和研究,使矿物成为矿床地球化学研究和矿床勘查的重要示踪剂。本文重点选择磁铁矿、磷灰石、石榴子石、榍石、锆石、绿泥石和绿帘石等的原位分析研究所获得的认识,介绍单颗粒矿物成分组合及变化在矿床类型划分、成矿年龄测定、氧逸度、成矿过程与物质来源、找矿与勘探等方面的应用。不同矿床类型中普遍存在的矿物,如磁铁矿、磷灰石等的微量元素含量及组合差异,提供了矿床类型识别的标志。单颗粒矿物,特别是矿石矿物和密切共生矿物如锡石、铌钽铁矿、赤铁矿、石榴子石、方解石等的原位定年,使成矿年龄的直接准确测定成为现实。矿物中变价元素,如Fe、V、Mn、Ce、Eu含量和/或比值的变化,指示了成矿过程氧逸度及其变化特点。从矿物核部向震荡环带与边部的微量元素含量或同位素组成的变化,示踪了成矿过程中流体来源或性质的变化。斑岩和矽卡岩矿床中与成矿作用关系密切的蚀变矿物,如绿泥石、绿帘石的形成温度、特征微量元素比值,如Ti/Sr、Ti/Co、V/Ni、Mg/Sr等,与距矿床中心距离呈线性函数关系,可定量预测距矿床中心的距离,使以绿泥石、绿帘石为代表的找矿指示矿物研究迅速发展。     

Mineralogy, Geochemistry, and Age Constraints on the Beni Bou Ifrour Skarn Type Magnetite Deposit, Northeastern Morocco

Abstract: The Beni Bou Ifrour deposit of northeastern Morocco is a skarn type magnetite deposit. K-Ar age determination suggests that the mineralization occurred at 7.040.47 Ma. The spatial relationship between skarn and dikes of microgran-odiorite derived from the batholith of Wiksane Granodiorite, and the similarity of age (8.020.22 Ma), confirms that the Wiksane Granodiorite is the igneous rock most probably related to mineralization. The skarn is distributed asymmetrically in the limestone, and magnetite ore was developed just below the calc-silicate skarn as two parallel beds separated by 100 m of barren limestone and schist.
The mineralization can be divided into three stages. The early stage is characterized by the formation of calc-silicate minerals, mainly clinopyroxene (80–70 % diopside) and garnet (early almost pure andradite to the late 60 % andradite). The main stage is characterized by the formation of a large amount of magnetite. Epidote and quartz formed simultaneously with magnetite. Fluid temperatures exceeded 500 C during the early to main stages. Fluid with very high salinity (50–75 wt% NaCl equiv.) was responsible for the formation of the magnetite ore. The oxygen isotope composition, together with the fluid inclusion data, suggests that magmatic fluid was significant for the formation of calc-silicate skarn minerals and magnetite. Low temperature (-230C) and low salinity (-10 % NaCl equiv.) hydrothermal fluids dominated by meteoric water were responsible for the late stage quartz and calcite formation.     

湘南黄沙坪多金属矿床花岗斑岩的矿物化学及其对矽卡岩白钨矿成矿的指示意义

黄沙坪多金属矿床是湖南最大的铅锌生产基地,并且在与矿床内花岗斑岩接触的矽卡岩带产有隐伏的大型矽卡岩型白钨矿和中型规模的辉钼矿。钨-钼矿化的时代为晚侏罗世,与矿床内花岗斑岩侵入时代一致。然而,已有研究认为,由于该花岗斑岩规模很小,矽卡岩型白钨矿的成矿热液应来自深部岩浆房而非此花岗斑岩。为此,我们对花岗斑岩进行了仔细的镜下观测,并且对其中的副矿物和黑云母以及矽卡岩中的白钨矿进行了电子探针成分分析,应用原位LA-ICP-MS方法测定了矽卡岩中白钨矿的稀土元素含量,试图对白钨矿矿化的物质和流体来源提供确切的证据。通过研究,首次在矿床内花岗斑岩中发现了与未蚀变黑云母伴生的黑钨矿和铌铁矿,表明花岗斑岩至少在岩浆结晶作用晚期或岩浆-热液过渡阶段早期就已发生钨的矿物富集,为确定花岗斑岩是控制钨矿化的成矿岩体提供了依据。此外,发现花岗斑岩中的黑云母(属铁叶云母)含有极高的氟含量(3%),指示其应形成于富含氟的高分异岩浆。研究进一步揭示,矽卡岩中白钨矿的轻稀土元素配分模式与花岗斑岩十分一致,而重稀土元素则显著亏损,而且Eu的含量较花岗斑岩更为富集。这暗示形成白钨矿的成矿流体应直接来自花岗斑岩,即:在早期无水矽卡岩阶段,石榴子石的沉淀导致流体中的重稀土亏损而Eu相对富集;白钨矿随后再从这种流体中沉淀。此外,白钨矿的Eu含量与Sm、Gd含量具有负相关关系,表明Eu的分配是相对独立的行为,主要以Eu2+存在,从而指示沉淀白钨矿的流体具有还原的性质。结合前人的研究成果及本文所提供的新证据,我们认为,形成矽卡岩型白钨矿的钨和成矿热液应来自高分异且富F的花岗斑岩,而所需的钙则可能来自于碳酸盐围岩,即矿床内花岗斑岩应是形成钨钼矿床的物质来源,驱动热液活动的能量来源,和寻找隐伏钨矿床的重要找矿标志。     

Fractured-controlled fluid flow and metasomatism in the contact aureole of the Marulan Batholith (New South Wales, Australia)

The Late Silurian Bungonia Limestone was contact metamorphosed adjacent to the Early Devonian Glenrock Granodiorite at 500-580 °C and 0.7-2.2 kbar. At >60 m from the granodiorite contact the limestone is pure calcite marble. Closer to the contact it was extensively metasomatised to form metre-scale dykes of garnet and clinopyroxene, massive wollastonite skarns, decimetre-thick veins dominated by vesuvianite, and distinct breccia zones that contain millimetre-wide veinlets of vesuvianite-garnet. These skarns and veins represent channel ways for aqueous Si-Mg-Fe-Al-bearing metasomatic fluids of magmatic origin. The '¹⁸O values of the marble are typically little reset (>20‰), even within millimetres of the skarn breccias, and only within tens of centimetres of the thicker skarns. The pattern of metasomatism and isotope resetting observed around and within the skarn zones does not accord with simple flow models that assume fluid flow from the granodiorite into marble that initially contained a connected, fluid-filled porosity. Instead, the data are most compatible with hydrofracture of corrosive, metasomatic fluids into initially dry rocks in short-duration flow events.