Does Tungsten Availability Control the Presence of Tungsten In Turbidite-Hosted Orogenic Gold Mineralization? Evidence From the Meguma and Bendigo-Ballarat Terranes
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Turbidite-hosted orogenic Au deposits are commonly enriched in W, along with a variety of other trace elements. A mineralogical source for W has recently been shown in the Otago Schist of southern New Zealand (Cave et al. 2016), with detrital rutile in the metasedimentary rocks recrystallizing to metamorphic titanite and making W available to be mobilized from the rock mass. In this study, we investigate the availability of W through prograde metamorphic mineral recrystallization in two additional turbidite-hosted orogenic Au provinces, one containing orogenic Au mineralization with associated subordinate W (Meguma Terrane, Canada), and the other containing orogenic Au mineralization without associated W (Bendigo-Ballarat Terrane, Australia). This was undertaken to assess whether W availability during prograde metamorphism is a key process in controlling the presence of W in turbidite-hosted orogenic Au mineralization. Like the Otago Schist, in both terranes detrital rutile is identified as being the most important host mineral for W in the lowest metamorphic grade rocks, and its prograde metamorphic recrystallization (to ilmenite) makes significant amounts of W available for mobilization (0.65 and 1.85 g of W per tonne of rock from the Goldenville and Halifax groups of the Meguma Terrane, respectively, and 0.16 g of W per tonne of rock from the Castlemaine Group of the Bendigo-Ballarat Terrane). This release of W in the Meguma Terrane is likely the source of W in these orogenic Au deposits. The lack of W in the orogenic Au deposits of the Bendigo-Ballarat Terrane suggests that W availability is not the only process controlling the presence of W minerals in turbidite-hosted orogenic Au mineralization. Alternatively, it might reflect a lower greenschist facies metasedimentary (Castlemaine Group) source for these deposits (i.e., a lower metamorphic grade source than the rutile to ilmenite conversion), as has been previously suggested.Metallogeny
Volcanic belt
Allanite
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Wolframite
Scheelite
Porphyritic
Batholith
Pegmatite
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Breccia
Stockwork
Greisen
Dike
Country rock
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Mineralization with ion adsorption rare earth elements (REEs) in the weathering profile of granitoid rocks from Nanling region of Southeast China is an important REE resource, especially for heavy REE (HREE) and Y. However, the Jurassic granites in Zhaibei which host the ion adsorption light REE (LREE) ores are rare. It is of peraluminous and high K calc-alkaline composition, which has similar geochemical features of high K2O + Na2O and Zr + Nb + Ce + Y contents and Ga/Al ratio to A-type granite. Based on the chemical discrimination criteria of Eby [Geology 20 (1992) 641], the Zhaibei granite belongs to A1-type and has similar source to ocean island basalts. The rock is enriched in LREE and contains abundant REE minerals including LREE-phosphates and halides. Minor LREE was also determined in the feldspar and biotite, which shows negligible and negative Eu anomalies, respectively. This indicates that the Zhaibei granite was generated by extreme differentiation of basaltic parent magmas. In contrast, granites associated with ion adsorption HREE ores contain amounts of HREE minerals, and show similar geochemical characteristics with fractionated felsic granites. Note that most Jurassic granitoids in the Nanling region contain no REE minerals and cannot produce REE mineralization. They belong to unfractionated M-, I- and S-type granites. Therefore, accumulation of REE in the weathering profile is controlled by primary REE mineral compositions in the granitoids. Intense fractional crystallization plays a role on REE enrichment in the Nanling granitoid rocks.
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Allanite
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The quartz vein-type Fanjiabu gold deposit is economically the most important gold deposit in the Sulu ultrahigh pressure metamorphic terrane,Jiaodong Peninsula.Cathodoluminescence images and trace element and U-Pb isotope compositions by laser ICP-MS indicate that zircons extracted from auriferous quartz veins are exclusively inherited magmatic zircons from wall rocks of gold veins,namely the Neoproterozoic biotite monzogranite.A total of 22 analyses on 22 zircon grains were made,and a concordant homogeneous group was formed by 15 analyses,and a weighted mean 206 Pb/238 U age of(726±14) Ma(MSWD=4.6)was yielded.The remaining 7 analyses are plotted in a discordia,with an upper intercept U-Pb age of(758± 25)Ma and lower intercept age of(123±11)Ma(MSWD=0.45).The lower intercept age is consistent with 40 Ar/ 39 Ar hornblende ages of(118.8±1.6)Ma to(117.5±1.5)Ma of lamprophyre dikes closely associated with gold veins,and is therefore interpreted as the timing of mineralization at the Fanjiabu gold deposit.Results of this investigation and previous studies suggest that gold mineralization in the Sulu and Jiaobei terranes were contemporaneous,taking place at ca.120 Ma and coincident temporarily with lithospheric thinning of the North China craton.This indicates that the Fanjiabu gold deposit and,by inference,other coeval deposits in the Sulu terrane were formed as a result of thinning of lithosphere mantle beneath the North China craton.Fluid inclusion and stable isotope data show that ore-forming fluids in the Fanjiabu gold deposit were characterized by middle to high temperature,high salinity(15.5% to 23.2%)(NaCleq)and low δ18OH2O(-3.84‰to-4.05‰)and δDH2O(-82.5‰to-80.8‰) values.Gold-bearing pyrite has negative δ34S values ranging from-5.5‰to-9.1‰.These are similar to hydrothermal fluids from hydrocarbon-bearing basins and imply that ore-forming fluids of the Fanjiabu gold deposit may have been mainly derived from the Mesozoic Jiaolai basin.The basinal fluids were channeled along the Wulian-Mishan fault and its secondary structures,when gold was leached from the basement rocks and precipitated in favorable structural sites under reduced conditions.In contrast,a large number of gold deposits in the Jiaobei terrane have low salinity,high δ18OH2O and δDH2O values,and positive δ34S values.Metallogenic differences of Early Cretaceous gold deposits between the Jiaobei and Sulu terranes were caused by distinct basement rocks,fluid sources,and ore-forming environments.
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Bixiling and Shuanghe are two typical outcrop areas in the Dabie ultrahigh-pressure (UHP) metamorphic terrane. Based on field outcrop observations and petrographic and petrochemical studies, the authors find that the rock association consists predominantly of eclogite, amphibolite, gneiss and foliated garnet-bearing granite. Eclogite has the characteristics of the crustal source and is considered to form by UHP metamorphism crustal rocks in the deep interior of the mantle; amphibolite is the product of retrogressive metamorphism of eclogites during exhumation of the plate; gneiss was produced by anatexis and progressive evolution of amphibolite in an ideal environment during exhumation; and foliated garnet-bearing granite is the result of partial melting of gneiss. In conclusion, there is a reworked in-situ relationship between eclogite and gneiss (and/or foliated garnet-bearing granite).
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巴斯铁列克钨多金属矿床位于新疆阿尔泰造山带南缘,是近年来在区内发现的首例中型钨多金属矿床。矿体主要产于二叠纪花岗岩与上志留统-下泥盆统康布铁堡组火山-沉积岩接触带的矽卡岩中。钨矿化与矿区花岗质岩石有明显的空间关系。然而,与钨矿化有关的花岗质岩石成因尚不清楚。本文对矿区出露的与矿化关系密切的黑云母花岗岩、二长花岗岩和二云母花岗岩进行了锆石U-Pb 年代学和岩石地球化学研究。3个样品的LA-ICP-MS锆石U-Pb加权平均年龄分别为282.3±3.2Ma、284.3±2.2Ma和284.8±2.3Ma,属早二叠世岩浆活动的产物,与成矿年龄一致。所有岩石具有高硅(SiO2=73.6%~78.3%)、富碱(K2O+Na2O=5.15%~9.62%)富钾(K2O/Na2O>1.1)、贫钙(CaO=0.19%~0.75%)和钛(TiO2=0.04%~0.24%)、弱过铝-强过铝质(A/CNK=1.01~1.39)特征。这些岩石稀土元素总量(∑REE)变化较大(变化于20.3×10-6~328×10-6),但二云母花岗岩显示轻重稀土元素分异不明显((La/Yb)N=0.96~2.06)、Eu强烈负异常(δEu=0.07~0.41)的深V型稀土元素分布特征,黑云母花岗岩和二长花岗岩显示轻稀土略富集((La/Yb)N分别为2.8~5.5和4.8~7.4)且Eu负异常(δEu=0.33~0.39和0.34~0.63)明显的右倾型稀土元素分布特征。所有样品均显示相对富集Rb、Th、U、Pb元素和相对亏损Nb、Ti、P、Sr、Ba元素,但二云母花岗岩中W含量(4.6×10-6~9.4×10-6)相对低于黑云母花岗岩和二长花岗岩中W含量(分别为15.1×10-6~168×10-6和8.4×10-6~16.0×10-6)。所有样品的锆石具有正的高εHf(t)值(+3.8~+11)和相对年轻的亏损地幔模式年龄(Hf的tDM2为0.60~1.0Ga)。以上特征说明,这些岩石属高钾钙碱性分异I-A过渡型花岗岩。结合区域地质背景,认为这些岩体是二叠纪时期后碰撞伸展环境下两个独立岩浆事件的产物,母岩浆均来源于新生地壳熔体与幔源岩浆,经过高度分异演化后结晶形成矿区岩石。花岗质岩浆活动为巴斯铁列克钨矿床提供了成矿物质,岩浆演化过程(结晶分异与熔体-流体作用)对成矿元素有富集作用。;The medium-sized Bastielieke tungsten polymetallic deposit is a newly discovered deposit in the Kelan Basin at the southern margin of Altay Orogenic Belt. The skarn hosted the orebody which is at the outer contact zone between the granitoids and volcanic-sedimentary rocks of the Upper Silurian to Lower Devonian Kangbutiebao Formation. Two-mica granite, biotite granite and monzogranite outcrop in the Bastielieke ore district showing obvious spacial relation to the hosted ore deposits. The petrogenesis of these rocks associated with the tungsten mineralization is indefinitive. LA-ICP-MS zircon U-Pb geochronology and geochemical analysis of major and trace elements and zircon Hf isotope are performed to discuss their petrogenesis. These granites show consistent weighted mean 206Pb/238U ages of 282.3±3.2Ma, 284.3±2.2Ma and 284.8±2.3Ma, respectively, which indicate that the Permian magmatic events at the southern margin of Altay is consistent to the ages of mineralization. These granitoids exhibit high SiO2 concentration (73.6%~78.3%), high total alkali (Na2O+K2O) (5.15%~9.62%) concentration and low CaO (0.19%~0.75%) and TiO2 (0.04%~0.24%) concentrations. In addition, they are enriched in potassium (K2O/Na2O=1.08~2.06) with high A/CNK values (1.01~1.39). The total REE contents of these granites vary from 20.3×10-6 to 328×10-6 with different chondrite-normalized REE patterns. The two-mica granite is characterized by low (La/Yb)N ration (0.96~2.06) with pronounced negative Eu anomaly from 0.07 to 0.41, and showing a deep V-type pattern. The biotite granite and monzogranite display enrichment of LREE with (La/Yb)N ration ranging from 2.8 to 5.5 and 4.8 to 7.4, and moderate negative Eu anomalies ranging from 0.33 to 0.39 and 0.34 to 0.63, respectively. All samples display noticeable negative anomalies of Nb, Ti, P, Sr, Ba and strong positive anomalies of Rb, Th, U and Pb. The two-mica granite has lower W concentrations varying from 4.6×10-6 to 9.4×10-6 than those in the biotite granite and monzogranite from 15.1×10-6 to 168×10-6 and 8.4×10-6 to 16.0×10-6, respectively. In addition, zircon εHf(t) values range from +3.8 to +11, two stage model ages (tDM2) ranging from 0.6Ga to 1.0Ga. The petrologic and geochemical data indicate that these rocks are high-K calc-alkaline and weak peraluminious to strongly peraluminous, which is similar to the geochemical behavior of the fractionated I-A type granitoids. Combined with regional geology, we suggest that they are derived from melting of the juvenile crust and mantle, and followed by subsequent crystallization fractionation in deeper magma chamber in a post-collision environment by two independent magmatic events. These granites provide key ore components for the formation of Bastielieke tungsten polymetallic deposit and preconcentrate tungsten by crystallization fractionation and melts-fluid exsolution.
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