Late Mesozoic magmatism at Xiaokelehe Cu Mo deposit in Great Xing'an Range, NE China: Geodynamic and metallogenic implications
Yuzhou FengHong‐Yuan ChenBing XiaoRucao LiChangzhou DengJinsheng HanGuanghui LiHuilin ShiChun‐Kit Lai
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Quartz monzonite
Diorite
Lile
Molybdenite
Geochronology
Quartz monzonite
Porphyritic
Dike
Anorthosite
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It is shown that post-island-arc intrusive magmatism of the West-Magnitogorsk Zone embraced the time from Late Devonian to Late Carbon. The new systematization scheme for all variety of intrusive formations is proposed based on the new geological-geochemical data and evolutionary-genetic reconstructions. It presents four discrete intrusive series: 1) gabbro-norite-diorite, 2) gabbro-diorite-granite, 3) peridotite-gabbro-diorite-granite, 4) lamprophyre-dolerite. Each series is characterized by original properties of the body’s morphology and rocks petrography, mineralogy and geochemistry.
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It is shown that post-island-arc intrusive magmatism of the West-Magnitogorsk Zone embraced the time from Late Devonian to Late Carbon. The new systematization scheme for all variety of intrusive formations is proposed based on the new geological-geochemical data and evolutionary-genetic reconstructions. It presents four discrete intrusive series: 1) gabbro-norite-diorite, 2) gabbro-diorite-granite, 3) peridotite-gabbro-diorite-granite, 4) lamprophyre-dolerite. Each series is characterized by original properties of the body’s morphology and rocks petrography, mineralogy and geochemistry.
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Norite
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Island arc
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Abstract The giant Pulang porphyry Cu-Au district (446.8 Mt at 0.52% Cu and 0.18 g/t Au) is located in the Yidun arc, eastern Tibet. The district is hosted in an intrusive complex comprising, in order of emplacement, premineralization fine-grained quartz diorite and coarse-grained quartz diorite, intermineralization quartz monzonite, and late-mineralization diorite porphyry, which were all emplaced at ca. 216 ± 2 Ma. Mafic magmatic enclaves are found in both the coarse-grained quartz diorite and quartz monzonite. The well-preserved primary mineral crystals in such a systematic magma series (including contemporaneous relatively mafic intrusions) with well-defined timing provide an excellent opportunity to investigate upper crustal magma reservoir processes, particularly to test the role of mafic magma recharge in porphyry Cu formation. Two groups of amphibole crystals, with different aluminum contents, are observed in these four rocks. Low-Al amphibole crystals (Аl2О3 = 6.2–7.6 wt %) with crystallization temperatures of ~780°C mainly occur in the coarse-grained quartz diorite and quartz monzonite, whereas high-Al amphibole crystals (Al2O3 = 8.0–13.3 wt %) with crystallization temperatures of ~900°C mainly occur in the fine-grained quartz diorite and diorite porphyry. These characteristics, together with detailed petrographic observations and mineral chemistry studies, indicate that the coarse-grained quartz diorite and quartz monzonite probably formed by crystal fractionation in the same felsic magma reservoir, whereas the fine-grained quartz diorite and diorite porphyry formed from relatively mafic magmas sourced from different magma reservoirs. The occurrence of mafic magmatic enclaves, disequilibrium phenocryst textures, and cumulate clots indicates that the coarse-grained quartz diorite and quartz monzonite evolved in an open crustal magma storage system through a combination of crystal fractionation and repeated mafic magma recharge. Mixing with incoming batches of hotter mafic magma is indicated by the appearance of abundant microtextures, such as reverse zoning (Na andesine core with Ca-rich andesine or labradorite rim overgrowth), sharp zoning (Ca-rich andesine or labradorite core with abrupt rimward anorthite decrease) and patchy core (Ca-rich andesine or labradorite and Na andesine patches) textured plagioclase, zoned amphibole, high-Al amphibole clots, skeletal biotite, and quartz ocelli (mantled quartz xenocrysts). Using available partitioning models for apatite crystals from the coarse-grained quartz diorite, quartz monzonite, and diorite porphyry, we estimated absolute magmatic S contents to be 20–100, 25–130, and >650 ppm, respectively. Estimates of absolute magmatic Cl contents for these three rocks are 1,000 ± 600, 1,800 ± 1,100, and 1,300 ± 1,000 ppm, respectively. The slight increase in both magmatic S and Cl contents from the premineralization coarse-grained quartz diorite magma to intermineralization quartz monzonite magma was probably due to repeated recharge of the relatively mafic diorite porphyry magma with higher S but similar Cl contents. Mass balance constraints on Cu, S, and Cl were used to estimate the minimum volume of magma required to form the Pulang porphyry Cu-Au deposit. Magma volume calculated using Cu mass balance constraints implies that a minimum of 21–36 km3 (median of 27 km3) of magma was required to provide the total of 2.3 Mt of Cu at Pulang. This magma volume can explain the Cl endowment of the deposit but is unlikely to supply the sulfur required. Recharge of 5–11 km3 of diorite porphyry magma to the felsic magma reservoir is adequate to account for the additional 6.5–15 Mt of S required at Pulang. Repeated diorite porphyry magma recharge may have supplied significant amounts of S and some Cl and rejuvenated the porphyry system, thus aiding formation of the large, long-lived magma reservoir that produced the porphyry Cu-Au deposit at Pulang.
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Quartz monzonite
Amphibole
Phenocryst
Felsic
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Diorite
Massif
Dike
Fractional crystallization (geology)
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Qorveh area (west Iran) belongs to the Sanandaj-Sirjan zone. Igneous activity resulted from subduction of Neo-Tethys beneath Iran microplate during Mesozoic and Cenozoic produced several intrusive and extrusive rocks throughout Sanandaj-Sirjan zone that convoluted intrusive complex in south of the study area is one of them. This complex is generally comprised of diorite, gabbro, monzonite, quartz-monzonite and quartz-monzodiorite. Several garnophyric granite veins penetrated into the diorite and gabbro in the complex. These granite veins are metaluminous (A/CNK=0.66-0.9), alkalic and have I-type and A-type granitiod geochemical characteristics. These samples have moderate REE contents (�REE=83-147 ppm), negative Eu anomaly (Eu/Eu * =0.4-0.7), high field strength elements (HFSE) Nb, Ta, Ti… contents (�HFSE=70-130 ppm) and high light rare earth elements to heavy rare earth elements (LREE/HREE) ratios (average 6 ppm). Basis on the mineralogical, petrological and geochemical studies, it is clear that crystal plays an important role in generation of this rock. Also, granite samples possess geochemical signatures of active continental margin (enriched in large ion lithophile elements (LILE) Rb, K, U, Sr, Cs and Th with respect to Nb and Ti) and a post-orogenic geodynamic environment.
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Diorite
Lile
Lithophile
Continental Margin
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Two wall-rock types of contrasting chemical composition host the causative Ruby Star quartz monzonite porphyry intrusion and hypogene mineralization at the Sierrita porphyry copper deposit. Vein-related hydrothermal alteration in the Harris Ranch quartz monzonite and biotite quartz diorite wall rocks consists of several mineralogically discrete assemblages. Temporal evolution of different alteration assemblages was established, in part, using petrographic relations within, and crosscutting relations among, individual veins. Temperature and salinity characteristics of hydrothermal fluids responsible for filling of individual veins were determined using primary fluid inclusions in vein-filling quartz. Each generation of primary vein filling introduced characteristic secondary fluid inclusions into earlier developed veins as well. Histograms of homogenization temperatures of primary and secondary fluid inclusions from different veins, and accompanying salinity data, permitted temporal correlations to be drawn between veins which either did not exhibit crosscutting relations in individual samples or which formed in different wall rocks and thus exhibited different alteration mineralogies.Evolution of hydrothermal activity in the area sampled commenced with potassic alteration in both quartz monzonite and quartz diorite wall rocks from 10 to 12 molal (37-41 wt %) NaCl equivalent fluids, inclusions of which homogenize by halite dissolution in the approximate temperature range 300 degrees to 370 degrees C. Salinities of later fluids were in the range 2 to 3 molal (10-15 wt %) NaCl equivalent with only minor salinity variations for the remaining time span monitored by this study. Homogenization temperatures of primary fluid inclusions in veins formed from these lower salinity fluids began near 400 degrees C and increased initially to approximately 430 degrees C where boiling occurred. The pressure defined by boiling of these fluids is about 330 bars. A continuous decrease in fluid inclusion homogenization temperatures followed down to about 300 degrees C, during which time deposition of quartz and K-feldspar with accessory biotite and/or hematite occurred in new and reopened veins in the quartz monzonite wall rock. Simultaneously in the quartz diorite, a sequence of veins and adjacent alteration halos formed, each consisting of an early assemblage of potassic affinity (quartz + biotite + K-feldspar + albite) which evolved to a propylitic assemblage (quartz + epidote + chlorite) as vein filling proceeded. With continued cooling of the solution below about 300 degrees C, muscovite took the place of K-feldspar as the stable potassium-bearing mineral in the quartz monzonite. An analogue to this late-stage quartz + muscovite veining in the quartz monzonite could not be established in the quartz diorite but may consist of zeolite (stilbite) + anhydrite.The bulk of hypogene copper mineralization in both wall-rock types was associated with approximately 2 molal (10 wt %) NaCl equivalent solutions. In the quartz diorite, significant chalcopyrite deposition is associated with fluid inclusions homogenizing from 370 degrees down to about 320 degrees C and always occurs with the later stage propylitic minerals in each vein. In the quartz monzonite wall rock, chalcopyrite was deposited during the transition from potassic and into phyllic alteration. Fluid inclusion homogenization temperatures for this mineralization range from about 330 degrees down to 200 degrees C. No primary chalcopyrite was seen to occur with earlier potassic veining formed from either high- or low-salinity fluids in the quartz monzonite. A very late stage of deposition of chalcopyrite, pyrite, and minor bornite filled the center of late phyllic veins in the quartz monzonite; correlated fluid inclusions have salinities from 1 to 5 molal (5-23 wt %) NaCl equivalent and homogenization temperatures in the range 140 degrees to 160 degrees C. The different alteration and sulfide mineral assemblages interpreted to have formed simultaneously in the two wall rocks of contrasting chemical character can be reasonably assigned to different chemical interactions of each rock type with similar, or equivalent, hydrothermal fluids.
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Abstract The Baishiding molybdenum deposit is located in the Central‐Middle Guangxi depression zone of the South China Caledonian fold zone. Orebodies occur as quartz‐molybdenite veins within the Guiling monzonite pluton and arkosic quartz sandstone of Zhengyuanling Group in the northeastern Guangxi. They are NEE‐trending with a dip angle of 75–80°. Zircon SHRIMP U‐Pb geochronologic analyses of the Guiling monzonite show age of 424.4 ± 5.6 Ma. It indicates that the Guiling monzonite was emplaced in Silurian. The ore minerals in quartz‐molybdenite veins contain molybdenite, pyrite, chalcopyrite and scheelite. Six molybdenite samples yield Re‐Os ages between 433.3 ± 6.3 Ma and 417.2 ± 5.7 Ma, with a weighted mean age of 424.6 ± 5.7 Ma, which agrees with the zircon age of the Guiling monzonite pluton. It suggests that the deposit was formed in the Silurian, not the Jurassic as previously thought. The Baishiding deposit is the only Silurian molybdenum deposit so far recognized in the South China. It was probably formed in a crustal shortening setting along the continental margin in the Silurian.
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