The Climax-Alma granite batholith of oligocene age and the prophyry molybdenum deposits of Climax, Colorado, U.S.A.

The porphyry molybdenum deposits of Climax, Colorado, are stockworks of quartz-molybdenite veinlets. They are apical to intrusive cupolas of leucocratic rhyolite-granite porphyry of Oligocene age (33 to 24 Ma). The upper parts of the orebodies are overprinted by overlying zones of phyllically altered rocks, and by stockworks of greisen-like veinlets, containing quartz, pyrite, topaz and huebnerite. The phyllic and/or greisen-like zones are surrounded by a propylitic zone, characterized by quartz-chlorite-hematite veinlets and chlorite after biotite. Late veins, radial and peripheral to the intrusive center, are common but widely scattered and discontinuous. Such veins typically contain quartz, fluorite, rhodochrosite, pyrite, dark sphalerite, galena, tetrahedrite, and traces of huebnerite, molybdenite, argentite, native gold and/or electrum.

The Alma district, 4 to 10 km southeast of Climax, contains widely scattered clusters of veins and replacement deposits. The veins cut chloritized to sericitized silicate host rocks, and the replacement deposits are in carbonate host rocks. The ore- and gangue-mineral assemblages of the veins of the Alma district resemble those of veins peripheral to the Climax molybdenum deposits. Veins of the Alma district cut dikes of Late white rhyolite (35 Ma), which resemble the rhyolite porphyries of Climax. A swarm of such dikes is parallel to the long axis of an elliptical drainage pattern, which bounds a structural dome, here called the outer Alma dome. The outer Alma dome (8 × 12 km) surrounds an inner Alma dome (6 × 8 km). Veins of the Alma district generally are axial and/or marginal to the outer Alma dome, and/or radial to the inner Alma dome. Veins and alteration minerals associated with the outer Alma dome formed between 35 and 27 Ma ago. Those associated with the inner Alma dome formed about 27 Ma ago, as indicated by fission-track age determinations on thermally annealed zircon grains from hydrothermally altered rocks, within and around the inner Alma dome.

Negative Bouguer gravity anomaly patterns indicate: (1) a regional, northeast-trending gravity low, associated with the composite monzonite-granodiorite-granite B batholith of the Colorado mineral belt (average density about 2.62 g/cm³); (2) a semi-regional gravity trough, within the gravity low of the Colorado mineral belt, extending northeastward across the Mosquito Range; (3) an oval pattern of gravity lows, coincident with the Alma domes; and (4) a closed gravity low associated with the Climax stock (density about 2.56 g/cm³) (Tweto and Case, 1972; Behrent and Bajwa, 1974; Corry, 1981).

The semi-regional gravity trough is interpreted as the gravimetric expression of a granite batholith, here called the Climax-Alma batholith. The gravity lows of the Climax and Alma districts are interpreted as expressions of cupolas on this granite batholith.

The highly differentiated rhyolite-granite intrusions of Climax plunge toward the Alma domes. The Climax intrusions are interpreted as products of apical differentiation of the inferred Climax-Alma granite batholith. Magmatic-hydrothermal fluids, associated with highly differentiated apical magmas, produced the Climax molybdenum orebodies. Most of the veins and replacement deposits of the Alma district are associated with lower, broader cupolas of the inferred granite batholith. The shape of the composite Climax-Alma magmatic-hydrothermal system resembles that of a teapot, with Climax above the spout and the Alma district above the lower, broadly domed lid.     

福建省上杭县罗卜岭斑岩铜钼矿床构造控矿规律研究

罗卜岭铜(钼)矿区位于紫金山矿田的东北部,是与晚中生代花岗闪长斑岩体有关的隐伏斑岩型铜钼矿床;主要斑岩矿体产于绿泥石化-绢英岩化和(弱)钾化-绢英岩化带中,矿石矿物组合为黄铜矿+辉钼矿;少量过渡类型矿体产于高级泥化带中,矿石矿物组合为蓝辉铜矿+铜蓝+辉钼矿。罗卜岭矿区地表露头含矿裂隙的统计结果显示,罗卜岭成矿晚期的含矿裂隙具有明显的方向性。远离斑岩体的含矿裂隙与其附近的区域构造方位或侵入体走向相近,表明受到北东向区域构造活动控制;而斑岩体西侧露头附近的含矿裂隙呈放射状,主要受到斑岩体侵入作用的影响。深部隐伏矿体则受到区域断裂和花岗闪长(斑)岩侵入体的共同控制,具体表现为:垂向上,以隐伏似斑状花岗闪长岩为中心,由深至浅,矿体铜钼品位比值依次变大,显示了Mo\Cu-Mo\Cu(Mo)的元素垂向分带;平面上,铜、钼元素沿着北东向、北西向断裂和岩体接触带附近有明显富集;斑岩型铜钼矿体主要产于似斑状花岗闪长岩外接触带的花岗闪长斑岩中,形态和产状受到区域北东向断裂或岩体接触带构造影响;蓝辉铜矿体主要产于罗卜岭花岗闪长斑岩外接触带的花岗闪长岩体内,形态和产状受接触带控制。区域构造和斑岩侵入体对斑岩型铜钼矿化有不同的影响,浅部铜、钼矿化受区域断裂构造控制作用明显,而深部矿体主要受花岗闪长(斑)岩体和断裂构造共同控制。区域上北东向背斜构造和北东、北西向断裂构造控制了花岗闪长质侵入岩体的侵位,矿区尺度的断裂构造对斑岩体的就位和成矿作用有一定的影响,罗卜岭花岗闪长斑岩体及其接触带则直接控制了斑岩型矿体的产出,这一规律对紫金山矿田深部和外围隐伏斑岩型矿体的勘查工作具有重要的参考意义。     

Structural analysis of faults related to a heterogeneous stress history: reconstruction of a dismembered gold deposit,Stawell, western Lachlan Fold Belt,Australia

In the internationally significant Victorian goldfields a complex system of faults dismembers the 5 million ounce Magdala gold deposit. These faults represent a combination of neoformed faults and inherited faults that reflect deformation associated with stress tensors of variable orientation and stress shape ratio (φ). The fault geometry is strongly controlled by the pre-existing rheology. Faults have propagated around the flanks of an antiformal basalt dome, along earlier ductile cleavages and the margins of porphyry dykes. Many of the faults do not have Andersonian geometries and there is no correlation between the orientation of the faults and the palaeostress directions. Much of the faulting is associated with the emplacement of porphyry dykes, additional gold mineralisation related to plutonism and late-stage deformation post-dating the intrusion of the Stawell pluton. Systematic mapping of extension veins associated with faults, striations and conjugate joint sets allowed the construction of a revised and more robust history of brittle deformation. This successfully predicted the offset direction of the currently mined Magdala ore body beneath the studied system of faults. The use of extension veins was a critical aspect of the analysis. If striations on the fault surfaces had solely been used, the offset direction of the new Golden Gift orebody would not have been correctly ascertained. The palaeostress history was delineated via use of compression and tension dihedra, stress inversion of slip data and calculation of theoretical resolved shear stress for faults with orientations similar to those mapped. The calculation of theoretical resolved shear stress directions highlights the importance that the intermediate stress has on the slip direction for faults whose pole does not lie in the plane containing σ₁ and σ₃.     

广西古袍金矿区花岗斑岩侵入期后多期热液成矿作用的Ar-Ar年龄证据

古袍矿区的花岗斑岩出露于古袍复向斜西部扬起部位。围岩地层主要为寒武系水口群浅变质砂岩、粉砂岩、硅质岩及板岩、千脉岩和破质页岩。花岗斑岩和花岗斑岩内的石英脉体中石英样品的40Ar/39Ar年龄数据表明户，40Ar/39Ar坪年龄值在187.87±1.53 Ma至244.88±2.48 Ma之间，是加里东期花岗斑岩成岩作用之后，海西、印支或者燕山早期多期构造热液作用的产物。金矿化与花岗斑岩成岩后的多期次构造热液作用有关。主要受控于断层破碎带及其中充填的石英脉和黄铁矿化。     

华南诸广山岩体中段岩脉40Ar-39Ar年龄及与铀成矿关系

诸广山岩体中段鹿井地区矿床周边常有花岗斑岩脉及煌斑岩脉等晚期岩脉产出。钾长石40Ar-39Ar同位素年代学测试结果表明,花岗斑岩脉与煌斑岩脉侵位年龄分别为116.24±0.49 Ma和128.27±0.86 Ma,是早白垩世地壳伸展的岩浆响应。岩脉记录的岩浆活动时代与鹿井矿田铀成矿作用时代具有较好的对应关系。花岗斑岩脉与铀矿石均具有幔源特征,表明以花岗斑岩为代表的酸性岩浆在为铀矿化提供热源的同时可能还提供了部分成矿物质。在铀成矿作用过程中,以煌斑岩为代表的基性岩浆为铀成矿作用提供了热源、矿化剂、流体及动力条件等有利条件。     

新疆西准噶尔克拉玛依岩体中暗色岩墙的形成时代及地质意义 ——来自锆石LA-ICP-MS和角闪石Ar-Ar定年的证据

新疆西准噶尔克拉玛依岩体以及周围地层中存在着大量暗色闪长玢岩岩墙,是岩浆物质贯入3组走向不同的裂隙形成的。对其中一个闪长玢岩岩墙样品进行锆石LA-ICP-MS年代学测试,得到303.1±1.2Ma的锆石²⁰⁶Pb/²³⁸U加权平均年龄,对从该闪长玢岩中分离出的角闪石进行Ar-Ar年代学测试,得到312.1±2.8Ma的坪年龄(1120～1400℃)和313.6±6.9Ma的反等时线年龄。对该闪长玢岩岩墙附近的含角闪石黑云母二长花岗岩进行的锆石LA-ICP-MS年代学测试,获得其²⁰⁶Pb/²³⁸U加权平均年龄为319.0±1.0Ma。对侵入石炭纪地层的一个花岗斑岩岩脉样品进行锆石LA-ICP-MS年代学测试,得到了315.3±1.0Ma的²⁰⁶Pb/²³⁸U加权平均年龄。上述年代学测试结果表明克拉玛依市以西地区的暗色岩墙形成时代是石炭纪末期,不是前人所说的二叠纪。在这些岩墙形成之前,该区在石炭纪晚期还发育以克拉玛依岩体及附近酸性岩脉为代表的花岗质岩浆活动。上述围岩和岩墙的年代学资料揭示出该区闪长玢岩岩墙所占据的裂隙形成时代在315～303Ma之间,为新疆西准噶尔地区晚古生代地球动力学背景及岩浆活动的深入研究,提供了时间方面的约束。     

致矿侵入体的识别标志——以新疆阿尔夏提矽卡岩型铁铜矿床为例

致矿侵入体的识别是成矿学研究和资源勘查的关键环节之一,对于许多矿床类型来说也是一个难点.本文以新疆阿尔夏提矽卡岩型铁铜矿床为例,阐述了通过建立五种联系及其地质学、岩石学、矿物学、地球化学和成矿学标志的识别方法,进而提出推木尔特岩基为含矿流体屏蔽层的认识.推木尔特岩基与矽卡岩矿体具有紧密的空间联系,容易被误认为是致矿侵入体.然而,其成岩时间早于成矿时间,仅导致围岩的大理岩化和角岩化,因而不是成矿物质的来源.相反,矿区内分布的闪长质小岩体和各类岩墙不仅与矿体和矽卡岩存在紧密的空间联系,而且岩石中普遍见有造矿矿物与造岩矿物的共结关系,岩体(墙)本身及其围岩也经受了强烈的流体改造,是含矿流体的通道和真正的致矿侵入体.     

哀牢山长安金矿成因机制及动力学背景初探：来自LA-ICP-MS锆石U-Pb定年和黄铁矿原位微量元素测定的证据

长安金矿床是哀牢山成矿带南段大型矿床之一,金矿化位于志留系、奥陶系之间发育的不整合面内,矿体整体呈透镜状。矿区内脉岩广布,矿体与脉岩共生或被脉岩切穿,表明金成矿与金沙江-哀牢山新生代富碱斑岩的侵入关系密切。本文在较为详细的野外观察基础上,对侵入矿体内的脉岩进行LA-ICP-MS U-Pb测年表明,细晶正长岩脉和正长斑岩的成岩年龄分别为32.5±0.1Ma和33.0±0.1Ma,与哀牢山的新生代富碱斑岩金多金属矿床的成矿时代(34±2Ma)基本一致。通过对长安金矿床、铜厂铜钼金矿床、长安冲铜钼金矿床中黄铁矿的LA-ICP-MS原位微量元素分析,发现黄铁矿中成矿元素含量随Co/Ni比值的下降而上升,呈一定的负相关性,可能指示其成矿物质主要来源于岩浆流体。结合前人的研究成果,表明喜山期强烈的壳幔作用导致大规模的富碱岩浆上侵,不仅为含矿流体的上升提供了动力和热能,而且还是成矿物质和成矿流体的主要来源。     

滇西北衙铁金多金属矿床成矿地质特征及其两阶段成矿过程研究——以万硐山矿段为例

滇西北衙铁金多金属矿床为西南三江富碱斑岩-多金属成矿带中南段典型矿床之一,成矿严格受富碱斑岩及其相关的深大断裂控制,伴随多期富碱斑岩脉体侵入、热液交代与围岩蚀变、矿物质富集及次生富集过程,构成了复杂的斑岩-矽卡岩成矿系统和地表次生成矿系统。文章以万硐山露天采场区大比例尺地质填图为基础,重新厘定和梳理各地质体及其间相互关系,取得了万硐山矿段详细的成矿地质特征及原生矿化的两阶段成矿新认识。     

浙西开化地区桐村花岗斑岩LA-ICP-MS 锆石U-Pb年龄及其地质意义

报道了浙西开化地区桐村含Cu、Mo花岗斑岩的LA-ICP-MS锆石U-Pb年龄,2个样品加权平均年龄介于167.6~155.6 Ma之间,反映花岗斑岩形成于中、晚侏罗世。该时期同时又是燕山运动活跃的时期,区域构造以北西—南东向挤压为特征,形成走向北东的压性断裂和配套的南东向张性断裂。2组断裂交会产生的应力薄弱区为燕山期发生的规模性岩浆活动提供了侵位通道。因此,浙西地区拥有良好的构造和岩浆成矿条件,成矿潜力巨大。     

U–Pb dating, Hf-isotope characteristics and trace-REE-patterns of zircons from Medet porphyry copper deposit, Bulgaria: implications for timing, duration and sources of ore-bearing magmatism

Precise U–Pb geochronology, Hf isotope compositions and trace element distributions in zircons are combined in the present study to define the timing and sources of the magmatism forming the Medet porphyry copper deposit, Bulgaria. ID-TIMS U–Pb-zircon dating demonstrates that ore-bearing magmatism extended for less than 1.12 Ma. As inferred from the field relationships, it started with the intrusion of a quartz-monzodiorite at 90.59?±?0.29 Ma followed by granodiorite porphyries at 90.47?±?0.30 and 90.27?±?0.60 Ma and by crosscutting aplite dykes at 90.12?±?0.36 Ma. These units were overprinted by potassic alteration and host economic copper-(Mo–Au) mineralization. The main magmatic–hydrothermal activity ceased after that, and a later quartz-granodiorite porphyry dyke, dated at 89.26?±?0.32 Ma, only contains an uneconomic quartz–pyrite mineralization. Assimilation of Lower Paleozoic rocks with a mantle to mantle–crust signature is characteristic of the fertile magma in the Medet deposit, as defined by positive ?-Hf values of the inherited zircons. The positive Ce-anomalies and the higher Eu/Eu* ratios of the zircons in the mineralized Cretaceous rocks of Medet deposit argue for crystallization from a generally more oxidized magma compared to the later quartz-granodiorite porphyry dyke. A change in paleostress conditions occurred during the intrusion of the Medet pluton and its dykes. The initial stage reveals E–W extension associated with N–S compression, whereas the younger granodiorite dyke was emplaced during subsequent N–S extension. The large-scale switch of the extensional stress regime during the mineralization was favourable for ore deposition by channelling the fluids and increasing the effective permeability.     

Rift-zone development around a plume-related magma centre on the Isle of Skye (Scotland): a model for stress inversions

ABSTRACT Using the example of the Isle of Skye in Scotland, we investigate the influence of pressure variations in upper-crustal magma reservoirs on the development of rift-type normal faulting around central volcanoes. The regional synmagmatic stress regime is of strike-slip type in Scotland during the Lower Tertiary. During a prolonged period of overall high pressure in the Skye magma reservoir (gabbro intrusion stage), crustal extension results from the injection of basaltic dykes parallel to the trend of the far-field maximum stress. During a subsequent period of pressure decrease in the reservoir (granites intrusion stage) normal faults trending parallel to the dykes are initiated. These faults tilt the upper-crustal blocks along with the former dyke swarm and associated lava pile. Finite-element modelling shows that a decrease of magma pressure in a circular cavity may lead, as in Skye, to a change from a regional strike-slip to a local rift-type normal stress regime.     

New geochronological results and structural evolution of the Pataz gold mining district: Implications for the timing and origin of the batholith-hosted veins

The Paleozoic Pataz–Parcoy gold mining area is located in a right-stepping jog on the regional Cordillera Blanca fault, in northern Peru. Most of the 8 million ounces of gold production from this area has come from quartz–carbonate–sulfide veins hosted by the Pataz batholith. Despite a subduction zone setting since at least the Cambrian, the area records several periods of extension and its present structure is that of a rift and graben terrain. The Pataz district (the northern part of the Pataz–Parcoy area) is dominated structurally by northwest to north northwest-striking (NW–NNW) faults and northeast to east northeast-striking (NE–ENE) lineaments, both of which have been active periodically since at least the Mississippian (Early Carboniferous). NW–NNW faults control the margins of a central horst that exposes basement schist and the Pataz batholith, and step across NE–ENE lineaments. The Lavasen graben, to the east of the central horst, contains the Lavasen Volcanics, and the Chagual graben, to the west, contains an allochthonous sedimentary sequence derived from the Western Andean Cordillera.New SHRIMP zircon geochronological data indicate emplacement of the Pataz batholith during the Middle Mississippian, at around 338–336 Ma, approximately 10 Ma earlier than previous estimates based on ⁴⁰Ar/³⁹Ar geochronology. The calc-alkaline, I-type batholith comprises diorite and granodiorite, the latter being the major component of the batholith, and was emplaced as a sill complex within the moderately NE-dipping sequence of the Eastern Andean Cordillera. Moderate- to high-temperature ductile deformation took place on the batholith contacts during or shortly after emplacement. Following emplacement of the batholith, differential uplift occurred along NW–NNW faults forming the Lavasen graben, into which the Lavasen Volcanics were deposited. SHRIMP U–Pb in zircon ages for the Lavasen Volcanics and the Esperanza subvolcanic complex, which was intruded into the western margin of the graben, are within error of one another at ca 334 Ma. The ductile batholith contacts were cut by renewed movement on NW–NNW faults such that the margins of the batholith are now controlled by these steep brittle-ductile faults. The NW–NNW faults were oriented normal to the principal axis of regional shortening (ENE–WSW) during formation of the batholith-hosted, gold-bearing quartz–carbonate–sulfide veins. The misoriented faults were unable to accommodate significant displacement, leading to high fluid pressures, vertical extension in the competent batholith and formation of gold-bearing veins. Brittle failure of the batholith was most extensive in the northern Pataz district where the fault-controlled western contact of the batholith is offset by a swarm of NE–ENE lineaments.The timing of vein formation is not established, despite published ⁴⁰Ar/³⁹Ar ages of 312 to 314 Ma for metasomatic white mica, which are interpreted as minimum ages of formation. Gold-bearing veins formed during or shortly after uplift of the Pataz batholith and formation of the Lavasen graben; they were therefore broadly coeval with deposition of the Lavasen Volcanics and emplacement of the Esperanza subvolcanic complex. These K-rich, weakly alkalic, ferroan (A-type) magmas may provide a viable source for the ore fluid that deposited gold in the Pataz batholith.     

Mineralization,alteration, structure,and Re–Os age of the Lanjiagou porphyry Mo deposit,North China Craton

Lanjiagou is a porphyry Mo deposit in terms of its alteration zonation and mineralization associated with granitic intrusions and predominance of quartz vein-hosted molybdenum mineralization. It is the largest Mo deposit in North China Craton (404,000 t). There is an intimate spatial/temporal association between all stages of mineralization and Early Jurassic granitic intrusions at Lanjiagou. Most of the molybdenum was emplaced during the principal hydrothermal (PH) stage (184.6 ± 1.3 – 185.6 ± 1.4 Ma), contemporaneously with intrusion of fine-grained porphyritic granite (188.9 ± 1.2 Ma) into a granite batholith (193 ± 3 Ma). The PH mineralization stage is mainly hosted by a quartz-dominated stockwork associated with phyllic alteration in the fine-grained porphyritic granite. This stage was followed by the late hydrothermal (LH) activity. Thick Mo-rich quartz veins were emplaced during the LH stage and cut the porphyry ore bodies. A ring breccia zone formed during the last hydrothermal stage and apparently cuts both the porphyry and the quartz vein ore bodies. The main hydrothermal vein stages have predominantly concentric and radial vein orientations centred on the ring breccia zone. Most of the concentric veins have shallow dips, whereas the radial veins are subvertical. The LH veins have predominantly NEE and NW orientations in the deposit and are moderately inclined. We surmise that the veining was controlled by the local stress regime generated by the intrusion of a large, deep pluton that we interpreted to be the source of the granites, the breccia zone, and the molybdenum mineralization. Resurgence within the magma chamber reactivated the steep concentric structures in a reverse sense, and accumulation of magmatic and/or fluid pressure resulted in explosive brecciation, producing the ring breccia zone. A predominantly late set of NW-trending, post-ore felsic dikes, associated with the regional structures, are a consequence of far-field stresses exceeding local stresses in the deposit.     

Petrology,geochemistry and zircon U–Pb and Lu–Hf isotopes of the Cretaceous dykes in the central North China Craton: Implications for magma genesis and gold metallogeny

The Trans-North China Orogen (TNCO), a Paleoproterozoic suture that amalgamates the Western and Eastern Blocks of the North China Craton (NCC), witnessed extensive magmatism and metallogeny during Mesozoic, associated with intraplate tectonics and differential destruction of the cratonic lithosphere. Here we investigate a suite of porphyry dykes surrounding the Mapeng batholith in the Fuping Complex within the TNCO in relation to the Mesozoic gold and molybdenum mineralization. The major element chemistry of these dykes show a range of SiO₂ (57.92 to 69.47 wt.%), Na₂O (3.20 to 4.77 wt.%), K₂O (3.12 to 4.60 wt.%) and MgO (0.51 to 3.67 wt.%), together with high concentration of LREE and LILE, and relatively low contents of HREE and HFSE. The rocks display (La/Yb)_N = 13.53–48.11, negative Nb, Ta, Th, U and Zr anomalies, and distinctly positive Ba, K and Sm anomalies. The mineralogy and geochemistry of the porphyry dykes indicate the rocks to be high-K calc-alkaline, and I-type, with adakitic features similar to those of the adjacent Mapeng batholith. The source magma for these rocks was derived from a mixture of reworked ancient continent crust and juvenile mantle materials. The zircon U–Pb data from these rocks show ages in the range of 124 to 129 Ma, broadly coinciding with the emplacement age of the Mapeng intrusion. The inherited zircons of ca. 2.5, 2.0 and 1.8 Ga in the dykes represent capture from the basement rocks during melting. The zircon Lu–Hf isotopic compositions show negative ε_Hf(t) values varying from − 27.8 to − 11.3, with Hf depleted model ages (t_DM) ranging from 1228 Ma to 1918 Ma and Hf crustal model ages (t_DM^C) of 1905 Ma to 2938 Ma, suggesting that the Mesozoic magmatism and associated metallogeny involved substantial recycling of ancient basement rocks of the NCC. We present an integrated model to evaluate the genesis of the porphyry systems and their relation to mineralization. We envisage that these dykes probably acted as stoppers (impermeable barriers) that prevented the leakage and run-off of the ore-bearing fluids, and played a key role in concentrating the gold and molybdenum mineralization.     

煌斑岩在玲珑金矿田形成过程中的地质意义

玲珑金矿田发育的金矿脉以黄铁石英脉为主.发育的含金石英脉在时空及成因方面与煌斑岩脉有密切联系.在空间上,煌斑岩脉与黄铁石英矿脉呈小角度相交,且大都错断矿脉.在时间上,同位素测年显示,煌斑岩脉的形成时间范围较大,一般为80～132Ma,而石英脉的形成主要集中在100～110Ma.通过煌斑岩中金含量测定及高温高压实验,煌斑岩并非是金元素的来源,金元素与煌斑岩在高温高压条件下不相溶,在成因方面,形成矿脉的大部分金元素与煌斑岩脉应同属于地幔物质;地幔岩浆含大量的地幔流体,根据金的化学性质,金易和地幔流体中的Cl-、OH-结合形成络合物,在地幔岩浆上侵过程中随地幔流体上升到地壳上部,并在适当的位置聚集形成含金石英矿脉,而煌斑岩浆从上侵的基性岩浆中分离出来,充填于构造裂隙中,形成煌斑岩脉.     

东沟含钼斑岩由太山庙岩基派生?

河南汝阳东沟斑岩型钼矿是近年来发现的超大型钼矿床,含钼斑岩被认为是太山庙岩基的岩枝或晚期分异产物.据此,东沟钼矿的形成似乎与太山庙岩基的岩浆分异作用有关.文章依据地质学、岩石学、岩石地球化学和温度场分析,认为东沟花岗斑岩是独立于太山庙岩基的另一次岩浆活动的产物.其依据为:①根据前人发表的测年结果,太山庙岩基和东沟斑岩体的形成时间相差约3 Ma,不应当认为形成时间一致;②太山庙岩基厚约3.5km,其出露高度大于东沟斑岩体,且东沟斑岩体距太山庙岩基约7 km,其问不存在大断裂,两者的空间分布关系不符合深部岩浆房分异模型;③东沟斑岩体含有高温石英斑晶,是高温岩浆固结的产物,而太山庙岩基是相对低温岩浆的深成侵入体;④以东沟斑岩体为中心分布有相对完整的同心环状Pb-Zn矿点,表明成矿时期存在由内向外逐渐降低的温度场.因此,东沟斑岩不应当是太山庙岩基的岩枝或晚期分异产物.此外,根据花岗质岩石钼平均丰度和含矿流体中钼溶解度的最新实验资料进行质量平衡计算,结果表明东沟斑岩不能提供足够的成矿物质,东沟钼矿的形成必须有额外的成矿物质来源.因此,东沟钼矿的成因与透岩浆流体成矿作用有关,岩浆体系和成矿体系是两个独立的地质体系.综合分析表明,岩浆来自大于30 km的下地壳,而成矿物质及流体具有多来源的特点.     

Controls on porphyry Cu mineralization around Hanza Mountain,south-east of Iran: An analysis of structural evolution from remote sensing,geophysical, geochemical and geological data

Hanza Mountain in Urmia–Dokhtar Magmatic Arc, southeast of Iran, consists of monocline of Eocene volcanic rocks into which the Oligocene granitoid rocks have been intruded. This area has excellent potential for economic porphyry copper deposits with Bondar Hanza, Daralu, and Sarmesk deposits among them. Hanza Mountain is located between NW–SE horsetail thrust faults derived from the Gowk and Sabzevaran strike-slip faults. The analysis of the kinematics of these strike-slip faults shows that they were not the cause of the formation of the pull-apart basin; thus they have not directly played any effective role in localizing the final emplacement of porphyries responsible for the formation of these copper deposits, but the Cu mineralization occurred mainly within a set of normal and thrust faults in the region. The alteration types and faults in Bondar Hanza were distinguished using detailed local geology, including distribution of known mineralization, supported by remote sensing (ASTER), airborne geophysics, and topography; the relationship between mineralization and faults was examined using Rose diagrams and Fry Analysis. This investigation of Bondar Hanza deposit has revealed that the trend of faults and dykes, as well as the distribution of copper analyses within drill cores, is aligned with the main trend of mineralization. The NW–SE trending faults in the Urmia–Dokhtar Magmatic Arc are effective in localizing the emplacement of porphyry copper ore deposits and those that trend between N125°–N145° are key to further exploration.     

浙西开化地区桐村花岗斑岩LA-ICP-MS锆石U-Pb年龄及其地质意义

报道了浙西开化地区桐村含Cu、Mo花岗斑岩的LA-ICP-MS锆石U-Pb年龄,2个样品加权平均年龄介于167.6～155.6Ma之间,反映花岗斑岩形成于中、晚侏罗世。该时期同时又是燕山运动活跃的时期,区域构造以北西—南东向挤压为特征,形成走向北东的压性断裂和配套的南东向张性断裂。2组断裂交会产生的应力薄弱区为燕山期发生的规模性岩浆活动提供了侵位通道。因此,浙西地区拥有良好的构造和岩浆成矿条件,成矿潜力巨大。     

The BanskáŠtiavnica ore district: relationship between metallogenetic processes and the geological evolution of a stratovolcano

The Banská?tiavnica ore district is in the central zone of the largest stratovolcano in the Central Slovakia Neogene Volcanic Field, which is situated at the inner side of the Carpathian arc over the Hercynian basement with the Late Paleozoic and Mesozoic sedimentary cover. Volcanic rocks of the High-K orogenic suite are of the Badenian through Pannonian age (16.5–8.5?Ma). Their petrogenesis is closely related to subduction of flysch belt oceanic basement underneath the advancing Carpathian arc and to back-arc extension processes. The stratovolcano includes a large caldera 20?km in diameter and a late-stage resurgent horst in its centre, exposing a basement and extensive subvolcanic intrusive complex. The following stages have been recognized in the evolution of the stratovolcano: (1)?formation of a large pyroxene/hornblende-pyroxene andesite stratovolcano; (2)?denudation, emplacement of a diorite intrusion; (3) emplacement of a large granodiorite bell-jar pluton within the basement; (4) emplacement of granodiorite/quartz-diorite porphyry stocks and dyke clusters around the pluton; (5) caldera subsidence and its filling by biotite-hornblende andesite volcanics, emplacement of quartz-diorite porphyry sills and dykes at the subvolcanic level; (6)?renewed activity of andesites from dispersed centres on slopes of the volcano; (7) uplift of a resurgent horst accompanied by rhyolite volcanics and granite porphyry dykes. The following types of ore deposits (mineralizations) have been identified in the Banská?tiavnica ore district: 1. Quartz-pyrophyllite-pyrite high-sulphidation system at ?obov, related to the diorite intrusion. 2. Magnetite skarn deposits and occurrences?at contacts of the granodiorite pluton with Mesozoic carbonate rocks. Magnetite ores occur as lenses in the calcic skarns. 3.?Stockwork/disseminated base metal deposit along an irregular network of fractures in apical parts of the granodiorite pluton and in remnants of basement rocks. Mineral paragenesis is simple, with leading sphalerite and galena and minor chalcopyrite and pyrite. In overlying andesites the mineralization is accompanied by metasomatic quartzites and argillites with pyrophyllite, kaolinite, illite and pyrite. 4. Porphyry/skarn copper deposits and occurrences related to granodiorite/quartz-diorite porphyry dyke clusters and stocks around the granodiorite intrusion. The mineralized zone is represented by accumulations of chalcopyrite in exo- and endo-skarns, usually of the magnesian type affected by serpentinization. Besides chalcopyrite, pyrhotite, minor bornite, chalcosite, tennantite and magnetite, rare molybdenite and gold are present. The alteration pattern around productive intrusions includes an external zone of propylitization, a zone of argillitic alteration (kaolinite – illite – pyrite) and an internal zone of phyllic alteration (quartz – sericite – pyrite). Biotitization is rare and limited to porphyry intrusions. 5. Intrusion related “mesothermal” gold deposit in an andesitic environment just above the granodiorite intrusion. Gold of high fineness with base metal mineralization is contained in brecciated and/or banded quartz veins of subhorizontal orientation, parallel to the surface of granodiorite pluton. At least the first phase of mineralization is older than quartz-diorite porphyry sills, which separate granodiorite and blocks of mineralized andesite. 6. Hot spring type advanced argillic systems in the caldera filling. Silicites and opalites accompanied by kaolinite, alunite and pyrite grade downward into smectite dominated argillites. 7. Vein type epithermal precious/base metal deposits and occurrences as a result of the long lasting interaction among structural evolution of the resurgent horst and evolving hydrothermal system, extensive intrusive complex and deep seated siliceous magma chamber serving as heat and magmatic fluid source. Three types of epithermal veins occur in a zonal arrangement: (a) base metal veins ± Au with transition to Cu?±?Bi mineralization at depth in the east/central part of the horst, (b)?Ag – Au veins with minor base metal mineralization and (c) Au – Ag veins located at marginal faults of the horst. Isotopic composition of oxygen and hydrogen in hydrothermal fluids indicate mixing of magmatic and meteoric component (with generally increasing proportion of meteoric component towards younger mineralization periods?). Veins are accompanied by zones of silicification, adularization and sericitization, indicating a low sulphidation environment. 8.?Replacement base metal mineralization of a limited extent in the Mesozoic carbonate rocks next to sulphide rich epithermal base metal veins.