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1.
Although volcanogenic massive sulfide (VMS) deposits can form within a wide variety of rift-related tectonic environments, most are preserved within suprasubduction affinity crust related to ocean closure. In stark contrast to the VMS-rich Appalachian sector of the Grampian-Taconic orogeny, VMS mineralization is rare in the peri-Laurentian British and Irish Caledonides. Economic peri-Gondwanan affinity deposits are limited to Avoca and Parys Mountain. The Tyrone Igneous Complex of Northern Ireland represents a ca. 484–464 Ma peri-Laurentian affinity arc–ophiolite complex and a possible broad correlative of the Buchans-Robert’s Arm belt of Newfoundland, host to some of the most metal-rich VMS deposits globally. Stratigraphic horizons prospective for VMS mineralization in the Tyrone Igneous Complex are associated with rift-related magmatism, hydrothermal alteration, synvolcanic faults, and high-level subvolcanic intrusions (gabbro, diorite, and/or tonalite). Locally intense hydrothermal alteration is characterized by Na-depletion, elevated SiO2, MgO, Ba/Sr, Bi, Sb, chlorite–carbonate–pyrite alteration index (CCPI) and Hashimoto alteration index (AI) values. Rift-related mafic lavas typically occur in the hanging wall sequences to base and precious metal mineralization, closely associated with ironstones and/or argillaceous sedimentary rocks representing low temperature hydrothermal venting and volcanic quiescence. In the ca. 475 Ma pre-collisional, calc-alkaline lower Tyrone Volcanic Group rift-related magmatism is characterized by abundant non-arc type Fe-Ti-rich eMORB, island-arc tholeiite, and low-Zr tholeiitic rhyolite breccias. These petrochemical characteristics are typical of units associated with VMS mineralization in bimodal mafic, primitive post-Archean arc terranes. Following arc-accretion at ca. 470 Ma, late rifting in the ensialic upper Tyrone Volcanic Group is dominated by OIB-like, subalkaline to alkali basalt and A-type, high-Zr rhyolites. These units are petrochemically favorable for Kuroko-type VMS mineralization in bimodal-felsic evolved arc terranes. The scarcity of discovered peri-Laurentian VMS mineralization in the British and Irish Caledonides is due to a combination of minimal exploration, poor-preservation of upper ophiolite sequences, and limited rifting in the Lough Nafooey arc of western Ireland. The geological and geochemical characteristics of the Tyrone Volcanic Group of Northern Ireland and peri-Gondwanan affinity arc/backarc sequences of Ireland and northwest Wales represent the most prospective sequences in the British and Irish Caledonides for VMS mineralization.  相似文献   

2.
The reason some VMS deposits contain more gold or other metals than others might be due to the influence of intrusions. A new approach examining this possibility is based on examining the information about many VMS deposits to test statistically if those with associated intrusions have significantly different grades or amounts of metals. A set of 632 VMS deposits with reported grades, tonnages, and information about the observed presence or absence of subvolcanic or plutonic intrusive bodies emplaced at or after VMS mineralization is statistically analyzed.Deposits with syn-mineralization or post-mineralization intrusions nearby have higher tonnages than deposits without reported intrusions, but the differences are not statistically significant. When both kinds of intrusions are reported, VMS deposit sizes are significantly higher than in the deposits without any intrusions. Gold, silver, zinc, lead, and copper average grades are not significantly different in the VMS deposits with nearby intrusions compared to deposits without regardless of relative age of intrusive. Only zinc and copper contents are significantly higher in VMS deposits with both kinds of intrusive reported. These differences in overall metal content are due to significantly larger deposit sizes of VMS deposits where both intrusive kinds are observed and reported, rather than any difference in metal grades.  相似文献   

3.
The Middle Cretaceous Cornucopia stock in the Blue Mountains of northeastern Oregon is a small composite intrusion consisting of hornblende biotite tonalite, biotite trondhjemite, and three cordierite two mica trondhjemite units. Unusual magnetite + biotite-rich tonalitic rocks are associated with the Crater Lake cordierite trondhjemite, the youngest of the intrusions. Oxide-rich tonalites are characterized by high Fe (~47-68 wt% total Fe as FeO), low SiO2 (<36 wt%), and enrichments in HFSE and REE (La(N)=361-903). Oxide-rich tonalites appear in a variety of forms, including composite dikes and sheets, in which they are associated with leucocratic tonalite. Leucotonalite is lower in SiO2 (60-72 wt%) than Crater Lake trondhjemite, and generally has DREE contents and Eu anomalies intermediate between the oxide-rich tonalite and Crater Lake compositions. Oxide-rich tonalites crosscut, and are crosscut by, shear zones in the host trondhjemite, indicating their emplacement late in the pluton's crystallization history. Granitic dikes crosscut the composite dikes in all localities. Geochemical considerations and sedimentary-like structures, such as load casts and bedding of magnetite-rich assemblages in the composite dikes and sheets, are suggestive of crystal settling from an Fe-rich parental magma. The Fe-rich liquid parental to the oxide-rich tonalite-leucotonalite pairs formed by extensive, in-situ, plagioclase + quartz-dominated crystallization of strongly peraluminous trondhjemite. Early magnetite saturation in the trondhjemite was suppressed, either because the parental trondhjemitic magma had a lower initial total Fe content or because it had a lower ferric-ferrous ratio, possibly reflecting a lower oxygen fugacity. Accumulation of magnetite from Fe-rich residual magma is a viable mechanism for the concentration of iron, and the subsequent formation of Fe-rich rocks, in calcic siliceous intrusions. Apparently, Fe-enrichment can occur locally in calcic magmas, and is not restricted to rocks of mafic tholeiitic or anorthositic affinity.  相似文献   

4.
Geological mapping and zircon U–Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) dating has identified a Mesoarchean (2857 ± 17 Ma) geological unit in the Luanjiajie area of the northern margin of the North China Craton, within the northern part of Liaoning Province, China. This unit is dominated by tonalitic and trondhjemite gneisses that form part of a typical tonalite–trondhjemite–granodiorite (TTG) rock assemblage. These Mesoarchean gneisses are enriched in Na and depleted in K, yield K2O/Na2O ratios of 0.34–0.50, have Rittmann index (σ) values of 1.54–3.04, and are calc-alkaline. They have EuN/EuN* values of 0.77–1.20 (average of 1.03), indicating that these samples have negligible Eu anomalies, and yield high LaN/YbN values (4.92–23.12). These characteristics indicate that these Mesoarchean gneisses have fractionated rare earth element (REE) compositions that are enriched in the light REE (LREE) and depleted in the heavy REE (HREE), with steeply dipping chondrite-normalized REE patterns. These gneisses are also enriched in Rb, Th, K, Zr, and Hf, and are relatively depleted in Ta, Nb, P, and Ti. In summary, the magma that formed these tonalitic and trondhjemite gneisses was most likely derived from the partial melting of lower-crustal basaltic rocks during subduction. The timing of formation (2.85 Ga) of the Luanjiajie tonalite and trondhjemite gneisses probably represents the timing of initiation of plate tectonics within the LongGang Block during a SE-directed subduction event. The presence of inherited zircons with ages of >3.0 Ga within the Luanjiajie gneisses suggests that this area may contain as yet undiscovered rocks that formed before 3.0 Ga.  相似文献   

5.
Rare earth elements, Rb, Sr, Ba and K have been determined in tonalite, trondhjemite, dacite, tholeiite and graywacke from the 2700 m.y. old Early Precambrian greenstone-granite terrane of northeastern Minnesota-northwestern Ontario, and also in trondhjemite from the 3550 m.y. old Morton Gneiss, southwestern Minnesota; and the Mesozoic Craggy Peak Pluton, Klamath Mountains, California.The Early Precambrian tholeiites have trace element compositions similar to modern oceanic tholeiites, while the quartz dioritic rocks, regardless of age, have total rare earth contents lower than that of tholeiitic basalts, with near chondritic heavy rare earth contents. Rb, Sr, Ba and K contents of the quartz diorites are about five times that of oceanic tholeiites, with similar alkali and alkaline earth ratios. The Early Precambrian graywacke has a rare earth content intermediate between greenstone and quartz diorite, reflecting its provenance.It is proposed that the analyzed quartz dioritic rocks, whether plutonic tonalite, dacite porphyry, gneissic or plutonic trondhjemite, or trondhjemite dikes had similar modes of origin, and were derived by partial melting of amphibolite or eclogite of basaltic or gabbroic composition at depths greater than thirty kilometers, leaving a residue consisting predominantly of garnet and clinopyroxene.  相似文献   

6.
The El Espino IOCG mining district is characterized by several mineralized bodies the largest of which is the El Espino deposit, which has an estimated geologic resource of 123 Mt at 0.66 % Cu and 0.24 g/t Au. Mineralized bodies are distributed in a 7?×?10 km2 area throughout a 1,000-m vertical section. They range from single veins to stockworks and breccias to manto-type deposits. The ore bodies are hosted primarily by volcanic, volcaniclastic, and sedimentary rocks of the Early Cretaceous Arqueros and Quebrada Marquesa formations, with a few mineralized zones within Late Cretaceous dioritic intrusions. The fault and vein architecture shows that El Espino IOCG system was localized within a dilatational jog along a major transtensional dextral fault system. Sodic alteration (albite) is the most extensive style of alteration in the district, and it is bounded by major NS–NNE trending faults. Sodic–calcic (epidote–albite) alteration occurs at deep to medium elevations (1,000–500 m) and grades inward into calcic alteration. Calcic alteration surrounds dioritic intrusions of the Llahuin plutonic suite. Significant iron oxides are associated with later calcic alteration associations (actinolite–epidote–hematite). The upper portions of the alteration system (0–500 m) display hydrolytic alteration associations with abundant hematite. Hydrolytic veins are feeders to zones of manto-type alteration and mineralization within favorable volcano-sedimentary lithologies that formed El Espino deposit. Sulfides are largely confined to calcic and hydrolytic alteration associations. Hydrothermal fluids responsible for hematite and sulfide mineralization had salinities between 32 and 34 wt% NaCleq and temperature of approximately 425 °C at an estimated depth of 3–4 km. Geochronological U–Pb and 40Ar/39Ar data indicate that hydrothermal alteration was coeval with magmatic intrusive activity. One particular dioritic intrusion (88.5 Ma) preceded the calcic stage (88.4 Ma), which was accompanied by iron oxide copper and gold mineralization. Hydrolytic alteration, related to economic iron oxide copper and gold mineralization, came immediately after at 87.9 Ma.  相似文献   

7.
The recently discovered Toki cluster, which includes the Toki, Quetena, Genoveva, Miranda, and Opache porphyry Cu–Mo prospects, is located 15 km south–southwest of the Chuquicamata–Radomiro Tomic mines in northern Chile. These prospects occur in an area of 5?×?6 km and are completely covered with Neogene alluvial deposits. Inferred resources for the cluster are estimated at about 20 Mt of fine copper, with Toki and Quetena contributing ～88 % of these resources. Mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the Collahuasi Group and intrusions of the Fortuna–Los Picos Granodioritic Complex. Hypogene mineralization in the Toki cluster consists mainly of chalcopyrite–bornite with minor molybdenite with mineralization grading outward to a chalcopyrite–pyrite zone and ultimately to a pyrite halo. Alteration is dominantly of the potassic type with K-feldspar and hydrothermal biotite. Sericitic alteration is relatively restricted to late quartz–pyrite veins (D-type veins). Previous K–Ar geochronology for the cluster yielded ages within a range of 34 to 40 Ma. Four new Re–Os ages for Toki indicate that molybdenite mineralization occurred in a single pulse at ～38 Ma. Re–Os ages for three different molybdenite samples from Quetena are within error of the Toki mineralization ages. These ages are concordant with a new zircon U–Pb age of 38.6?±?0.7 Ma from the tonalite porphyry in Quetena. Two Re–Os ages for Genoveva (38.1?±?0.2 and 38.0?±?0.2 Ma) are also within error of the Toki and Quetena molybdenite ages. Four Re–Os molybdenite ages for Opache range between 36.4 and 37.6 Ma. The Miranda prospect is the youngest with an age of ～36 Ma. Four new Re–Os ages for the Chuquicamata deposit range between 33 and 32 Ma, whereas nine new 40Ar/39Ar ages of biotite, muscovite, and K-feldspar range between 32 and 31 Ma. Analyzed molybdenites have Re and Os concentrations that vary between 21–3,099 ppm and 8–1,231 ppb, respectively. The highest Re and Os concentrations are found in the Toki prospect. Three new 40Ar/39Ar ages for the Toki cluster are younger than the Re–Os mineralization ages. The age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 Ma that probably reflect a late hydrothermal phyllic event. The new geochronological data presented here for the Toki cluster indicate that molybdenite mineralization occurred within a very short period, probably within 2 Ma, and synchronously (at ～38 Ma) in three mineralization centers (Toki, Quetena, and Genoveva). Furthermore, mineralization at the Toki cluster preceded the emplacement of the Chuquicamata deposit (35–31 Ma) and indicates that porphyry Cu–Mo mineralization occurred episodically over a period of several million years in the Chuquicamata district.  相似文献   

8.
土屋斑岩铜矿床位于新疆东天山晚古生代大南湖-头苏泉岛弧中.矿区出露地层为石炭系企鹅山群火山-沉积岩.文章提出矿区出露的火山-沉积岩以及浅成侵入岩为一火山-侵入杂岩体,发育2个旋回4个岩相:第一旋回包括溢流相玄武岩和安山岩、爆发相集块角砾熔岩和爆发-沉积相凝灰岩;第二旋回包括次火山相闪长玢岩和玄武玢岩.斜长花岗斑岩侵入到火山机构断裂系中.矿体赋存于斜长花岗斑岩和闪长玢岩中.斜长花岗斑岩为成矿斑岩,次火山岩相闪长玢岩为容矿岩石,火山岩为围岩.土屋斑岩铜矿床可分为前成矿期和主成矿期.前成矿期形成于火山活动的晚期,发育青磐岩化;主成矿期形成于斜长花岗斑岩侵位时期,发育钾硅酸盐蚀变、绿泥石-绢云母蚀变和黄铁绢英岩化蚀变及与之有关的矿化,形成了土屋斑岩型矿化的主体.矿化阶段包括钾硅酸盐阶段、绿泥石-绢云母阶段和黄铁绢英岩化阶段等.  相似文献   

9.
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.  相似文献   

10.
Eastern Iran has great potential for the discovery of different types of mineralization. The study area encompasses Tertiary magmatism in the northern Lut block located in northern Khur, South Khorasan, eastern Iran and is mostly covered by volcanic rocks, which are intruded by porphyritic subvolcanic intrusions in some places. Application of the spectral angle mapper (SAM) technique to Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images detected sericitic, argillic, and propylitic alterations, silicification, and secondary iron oxides. The alteration is linear and associated within vein-type mineralization. Twelve prospective areas are selected for detailed exploration and based on our processing results, in addition to NW-SE faults, which are associated with Cu mineralization indications, NE-SW faults are also shown to be important. Based on the presence of subvolcanic rocks and numerous Cu ± Pb-Zn vein-type mineralizations, extensive alteration, high anomaly of Cu and Zn (up to 100 ppm), the age (43.6 to 31.4 Ma) and the initial 87Sr/86Sr ratio (0.7047 to 0.7065) of the igneous rocks, and the metallogenic epoch of the Lut block (middle Eocene-lower Oligocene) for the formation of porphyry Cu and epithermal deposits, the studied area shows great potential for porphyry copper deposits.  相似文献   

11.
The dominantly high-K, moderate to high SiO2 containing, variably fractionated, volcanic-arc granitoids (± sheared) from parts of Bundelkhand craton, northcentral India are observed to contain molybdenite (Mo) in widely separated 23 locations in the form of specks, pockets, clots and stringers along with quartz ± pyrite ± arsenopyrite ± chalcopyrite ± bornite ± covellite ± galena ± sphalerite and in invisible form as well. The molybdenite mineralization is predominantly associated with Bundelkhand Tectonic Zone, Raksa Shear Zone, and localized shear zones. The incidence of molybdenite is also observed within sheared quartz and tonalite–trondhjemite–granodiorite (TTG) gneisses. The fluid inclusion data show the presence of bi-phase (H2O–CO2), hypersaline and moderate temperature (100°–300°C) primary stretched fluid inclusions suggesting a possible hydrothermal origin for the Mo-bearing quartz occurring within variably deformed different granitoids variants of Archean Bundelkhand craton.  相似文献   

12.
Whole rock oxygen isotope data are presented for the Panorama district, in the Archean Pilbara Craton of Western Australia, where near-perfect exposure reveals a cross section through a complete volcanogenic massive sulfide (VMS) hydrothermal alteration system. The δ18O values decrease with depth in the volcanic pile, across semi-conformable alteration zones, to values below 6‰ immediately above a large (180 km2) subvolcanic intrusion. Altered rocks in the upper parts of the subvolcanic intrusion have lower δ18O values (6–8‰) than least altered granite (8‰), apart from sericite–quartz altered zones, which are slightly higher (8–10‰). Corridors of low δ18O values crosscut this regional zonation, and are coincident with transgressive feldspar-destructive alteration zones, which underlie VMS mineralization. The whole rock oxygen isotope distribution patterns are interpreted to represent alteration temperature, where high δ18O values correspond to low temperature alteration and low δ18O values correspond to high temperature alteration. Alteration temperatures, which were calculated using modal alteration mineral abundances and an assumed fluid δ18O, are consistent with this interpretation. Increasing temperatures with depth in the volcanic pile and high temperatures in transgressive corridors leading up to VMS deposits, are consistent with a convective hydrothermal model, in which heat from the subvolcanic intrusion drove seawater through the volcanic pile. Granite-hosted sericite–quartz alteration zones are 18O-enriched, and are tentatively interpreted to have formed from a mixed magmatic-evolved seawater fluid. Received: 12 April 1999 / Accepted: 6 April 2000  相似文献   

13.
The Daero Paulos porphyry copper prospect, in the Asmara region of the central Eritrean highlands, is part of the Nakfa tectono-stratigraphic terrane, which, along with four other major and several minor terranes that constitute the Neoproterozoic Arabian-Nubian Shield, is characterized by juvenile, intra-oceanic island-arc crust. Alteration and mineralization at Daero Paulos occupy a north-northeast-trending corridor of multiphase, rhyolitic to dacitic intrusions emplaced into mafic and intermediate volcanic and subvolcanic rocks and derivative volcaniclastic strata. New U-Pb geochronological data for the volcanic rocks in the region confirm a >860-Ma age for the Neoproterozoic (Tonian) host sequence. The porphyry copper alteration evolved from early epidote-chlorite-albite through sericite-chlorite to late quartz-sericite. Local advanced argillic alteration is the erosional remnant of the lithocap that formerly dominated the shallow parts of the Daero Paulos system. A post-mineralization, Alaskan-type pyroxenite-gabbro body intruded the porphyry copper corridor, and is interpreted as the feeder for mafic dikes along the periphery of the porphyry copper system. Re-Os ages of 881.0 ± 5.5 and 864.2 ± 3.6 Ma for molybdenite from veinlets at Daero Paulos constrain an early Tonian timing for porphyry copper formation during early opening of the Mozambique Ocean after Rodinian supercontinent break-up. The ages also imply a rapid transition from initial rifting to the start of subduction and consequent establishment of an intra-oceanic island arc in what is now the Nakfa terrane. The molybdenite ages show that Daero Paulos is currently the oldest dated mineralization in the Arabian-Nubian Shield, and ~60–200 and, possibly, ~250 m.yr. older than porphyry copper mineralization elsewhere in the Shield. However, volcanogenic massive sulfide (VMS) mineralization could have been forming at broadly the same time, albeit not genetically associated with Daero Paulos. Preservation of such shallowly formed Neoproterozoic mineralization is mainly attributed to burial beneath thick post-amalgamation volcano-sedimentary basinal cover, collision-generated thrust sheets, and later Phanerozoic strata.  相似文献   

14.
《Ore Geology Reviews》2003,22(1-2):61-90
Quantitative laser ablation (LA)-ICP-MS analyses of fluid inclusions, trace element chemistry of sulfides, stable isotope (S), and Pb isotopes have been used to discriminate the formation of two contrasting mineralization styles and to evaluate the origin of the Cu and Au at Mt Morgan.The Mt Morgan Au–Cu deposit is hosted by Devonian felsic volcanic rocks that have been intruded by multiple phases of the Mt Morgan Tonalite, a low-K, low-Al2O3 tonalite–trondhjemite–dacite (TTD) complex. An early, barren massive sulfide mineralization with stringer veins is conforming to VHMS sub-seafloor replacement processes, whereas the high-grade Au–Cu ore is associated with a later quartz–chalcopyrite–pyrite stockwork mineralization that is related to intrusive phases of the Tonalite complex. LA-ICP-MS fluid inclusion analyses reveal high As (avg. 8850 ppm) and Sb (avg. 140 ppm) for the Au–Cu mineralization and 5 to 10 times higher Cu concentration than in the fluids associated with the massive pyrite mineralization. Overall, the hydrothermal system of Mt Morgan is characterized by low average fluid salinities in both mineralization styles (45–80% seawater salinity) and temperatures of 210 to 270 °C estimated from fluid inclusions. Laser Raman Spectroscopic analysis indicates a consistent and uniform array of CO2-bearing fluids. Comparison with active submarine hydrothermal vents shows an enrichment of the Mt Morgan fluids in base metals. Therefore, a seawater-dominated fluid is assumed for the barren massive sulfide mineralization, whereas magmatic volatile contributions are implied for the intrusive related mineralization. Condensation of magmatic vapor into a seawater-dominated environment explains the CO2 occurrence, the low salinities, and the enriched base and precious metal fluid composition that is associated with the Au–Cu mineralization. The sulfur isotope signature of pyrite and chalcopyrite is composed of fractionated Devonian seawater and oxidized magmatic fluids or remobilized sulfur from existing sulfides. Pb isotopes indicate that Au and Cu originated from the Mt Morgan intrusions and a particular volcanic strata that shows elevated Cu background.  相似文献   

15.
Wulaga epithermal gold deposit is located in northeast China. Gold mineralization mainly occurs within the crypto‐explosive breccia belt of subvolcanic intrusion. Constraints on the precise timing of mineralization are of fundamental importance for understanding the ore genesis of the Wulaga gold deposit and its mineralization potential. Three hydrothermal stages have been identified: the early veiny quartz–euhedral pyrite stage; the fine pyrite–marcasite–gray or black chalcedony stage; and the late carbonate–pyrite stage. The Rb–Sr dating of gold‐bearing pyrites from the fine pyrite–marcasite–gray or black chalcedony stage is 113.8 ± 4.4 Ma with an initial 87Sr/86Sr ratio of 0.706346 ± 0.000019. The age of the gold deposit is consistent with the age of ore‐bearing volcanic (109–113 Ma) and subvolcanic intrusion (103–112 Ma) within the error limits, and the pyrite initial ratio has an identical value of 87Sr/86Sr to subvolcanic intrusion (0.705547 ± 0.000012). These indicate that crystallization of the wall rock and epithermal gold mineralization was coeval and likely cogenetic. Moreover, a lot of epithermal gold deposits that formed in Early Cretaceous volcanic and subvolcanic intrusions have been discovered in recent years in Heilongjiang province. Combined with the studies of tectonic and magmatic activities, we propose that the formation of the Wulaga gold deposit might be caused by the heated circum‐flow water related to the volcanic–subvolcanic intrusive hydrothermal event triggered by the ancient subduction of the Izanagi plate in the Early Cretaceous.  相似文献   

16.
Four of the major plutons in the vicinity of the Candelaria mine (470 Mt at 0.95% Cu, 0.22 g/t Au, 3.1 g/t Ag) and a dike–sill system exposed in the Candelaria open pit have been dated with the U–Pb zircon method. The new geochronological data indicate that dacite magmatism around 123 Ma preceded the crystallization of hornblende diorite (Khd) at 118 ± 1 Ma, quartz–monzonite porphyry (Kqm) at 116.3 ± 0.4 Ma, monzodiorite (Kmd) at 115.5 ± 0.4 Ma, and tonalite (Kt) at 110.7 ± 0.4 Ma. The new ages of the plutons are consistent with field relationships regarding the relative timing of emplacement. Plutonism temporally overlaps with the iron oxide Cu–Au mineralization (Re–Os molybdenite ages at ∼115 Ma) and silicate alteration (ages mainly from 114 to 116 and 110 to 112 Ma) in the Candelaria–Punta del Cobre district. The dated dacite porphyry and hornblende diorite intrusions preceded the ore formation. A genetic link of the metallic mineralization with the quartz–monzonite porphyry and/or the monzodiorite is likely. Both of these metaluminous, shoshonitic (high-K) intrusions could have provided energy and contributed fluids, metals, and sulfur to the hydrothermal system that caused the iron oxide Cu–Au mineralization. The age of the tonalite at 110.7 Ma falls in the same range as the late alteration at 110 to 112 Ma. Tonalite emplacement may have sustained existing or driven newly developed hydrothermal cells that caused this late alteration or modified 40Ar/39Ar and K/Ar systematic in some areas.  相似文献   

17.
The Ansil Cu–Au volcanogenic massive sulfide deposit is located within an Archean-age cauldron infill sequence that contains the well-known Noranda base metal mining district. The deposit is unusual in that 17% of the massive pyrrhotite–chalcopyrite orebody is replaced by semi-massive to massive magnetite. Temporally associated with the magnetite formation are several calc-silicate mineral assemblages within the massive sulfide lens and the underlying sulfide stockwork vein system. Coarse-grained andradite–hedenbergite and ferroactinolite–ilvaite alteration facies formed in the immediate footwall to the massive magnetite–sulfide lens, whereas an epidote–albite–pyrite-rich mineral assemblage overprints the margins of the chlorite-rich stockwork zone. The epidote-rich facies is in turn overprinted by a retrograde chlorite–magnetite–calcite mineral assemblage, and the andradite–hedenbergite is overprinted first by ferroactinolite–ilvaite, followed by semi-massive to massive magnetite. The footwall sulfide- and magnetite-rich alteration facies are truncated by a late phase of the Flavrian synvolcanic tonalite–trondhjemite complex. Early phases of this intrusive complex are affected to varying degrees by calc-silicate-rich mineral assemblages that are commonly confined to miarolitic cavities, pipe vesicles and veins. The vein trends parallel the orientation of synvolcanic faults that controlled volcanism and hydrothermal fluid migration in the overlying cauldron succession. The magnetite-rich calc-silicate alteration facies are compositionally similar to those of volcanic-hosted Ca–Fe-rich skarn systems typical of oceanic arc terranes. Tonalite–trondhjemite phases of the Flavrian complex intruded to within 400 m of the base of the earlier-formed Ansil deposit. The low-Al trondhjemites generated relatively oxidized, acidic, Ca–Fe-rich magmatic–hydrothermal fluids either through interaction with convecting seawater, or by assimilation of previously altered rocks. These fluids migrated upsection along synvolcanic faults that controlled the formation of the original volcanogenic massive sulfide deposit. This is one of the few documented examples of intense metasomatism of a VMS orebody by magmatic–hydrothermal fluids exsolved from a relatively primitive composite sub-seafloor intrusion. Received: 15 April 1999 / Accepted: 20 January 2000  相似文献   

18.
在华北地台北缘中新生代火山岩发育区,发现大型铀钼矿床,其外围被第四系广泛覆盖。为了进一步扩大找矿,我们采用了以遥感图象、地质图件、航磁、航放资料为基础信息的多元信息计算机综合分析技术。通过已知成矿模式的建立,对与成矿有关的地质体与基础信息源之间的相关性研究,对这些相关信息在图像处理系统中进行的组合显示分析,从而确立了各类地质体及控矿地质要素复合集聚区的多参数影像模型;查明了它们的空间分布规律;圈出了5个主体火山机构;发现了大规模蚀变带及其与铀矿化异常之间的空间相关关系。据此编制出反映该区成矿地质环境的第四系覆盖层下深部地质构造影像图及成矿远景区影像图,在某一远景区内用航空彩色红外图像及侧视雷达图像进行解译,圈定了5个隐伏次火山岩体。经钻探验证了它们的存在并发现工业铀矿化。这一切都为已知矿区的外围扩大找矿工作起了指导作用。  相似文献   

19.
新疆阿舍勒盆地泥盆纪火成岩与构造-岩浆演化   总被引：1，自引：0，他引：1  
阿舍勒泥盆纪火山盆地是阿尔泰西南缘重要的矿集区,产出我国著名的火山成因块状硫化物型(VMS)矿床——阿舍勒铜矿.其内部发育的火山岩和侵入岩地球化学特征记录了阿舍勒盆地的构造岩浆演化和成岩、成矿作用过程,但其形成构造背景和成岩成矿机制一直存在争论.本文报道了阿舍勒矿集区萨尔朔克铜金多金属矿区深部英云闪长岩的LA-MC-I...  相似文献   

20.
In the Cretaceous Ningwu volcano-sedimentary basin in the Yangtze River Valley metallogenic belt, eastern China, there are three areas with a dense distribution of magnetite or hematite deposits: the Meishan deposit in the north; Washan, Nanshan and Taocun deposits in the center; and the Zhongjiu and Gushan deposits in the south. The mineralization in the Ningwu basin is associated mainly with subvolcanic intrusions, consisting of gabbro–diorite porphyry and/or gabbro–diorite. Alteration zoning of these deposits is pronounced, and includes: (1) an upper light colored zone of argillic, kaolinite, silica, carbonate and pyritic alteration (2) a middle dark colored zone of diopside, fluorapatite–magnetite, phlogopite, and garnet with fluorapatite–magnetite; (3) a lower light colored zone of extensive albitic alteration. However, at the Gushan iron deposit, the lower light colored zone and the middle dark colored zone are absent, whereas the principal alteration is represented by silicification, kaolinization, and carbonatization.The iron oxide–apatite deposits in the Ningwu basin are typically magmatic–metasomatic origin and are similar to the Kiruna-type deposits in Scandinavia, particularly with respect to mineral assemblages, fabric and structure of the iron ores, occurrence of the orebodies and wall rock alteration. The iron oxide–apatite deposits of the Ningwu basin contain magnetite and/or hematite, with diopside or actinolite and apatite gangue. They were formed in a rift or extensional environment and the mineralization is associated with alkaline magmatism. The time interval between magmatism and related mineralization is very short.  相似文献   

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