Prospectivity modeling of porphyry copper deposits: recognition of efficient mono- and multi-element geochemical signatures in the Varzaghan district,NW Iran

Acta Geochimica - The Varzaghan district at the northwestern margin of the Urumieh–Dokhtar magmatic arc, is considered a promising area for the exploration of porphyry Cu deposits in Iran. In...     

斑岩铜矿床成矿流体演化:中甸普朗铜矿床蚀变矿物学与热力学模拟

不同阶段热液蚀变矿物的组成是水岩反应过程和成矿流体演化的地球化学"指纹"。三江特提斯义敦岛弧南缘的普朗超大型斑岩铜矿床形成于晚三叠世甘孜-理塘洋西向俯冲的岛弧环境,但具有不同于典型斑岩铜矿的蚀变-矿化分带特征:即在早期钾硅酸盐化蚀变带内常可见晚期脉状(沿裂隙分布的细脉状)青磐岩化或沿破碎带边部发育的绢英岩化,且主要在青磐岩化蚀变带内发育铜(-钼)矿化。为此,本研究选取普朗矿床含矿石英二长斑岩(QMP)中热液黑云母及绿泥石进行矿物产状、共生组合和世代划分研究,并针对不同产状的绿泥石开展电子探针分析研究,以探讨其形成的物理化学条件,并结合热力学模拟结果反演成矿流体演化轨迹。不同于岩浆黑云母(Bt-1)的锯齿状边缘及内部发育磷灰石包体特征,普朗铜矿热液黑云母(Bt-2)多为片状且解理发育、沿其边缘或裂隙多被绿泥石交代。青磐岩化带内发育有两类产状明显不同的绿泥石,即由黑云母蚀变而成的片状绿泥石(Chl-1)和蠕虫状绿泥石(Chl-2),且后者多与黄铜矿、黄铁矿、磁黄铁矿及辉钼矿伴生。电子探针分析结果显示两类绿泥石均为富Mg的三八面体类绿泥石,且具有相似的主量元素组成。石英二长斑岩中Bt-2型黑云母形成温度范围为305-336℃(平均值为321℃),氧逸度位于NNO(Ni-NiO)缓冲线与HM(Fe_2O_3-Fe_3O_4)缓冲线之间。Chl-1和Chl-2型绿泥石形成温度分别为284～347℃(平均值为316℃)和278～328℃之间(平均值为310℃)。Chl-1和Chl-2的Log f_(O_2)分别在-42.7--37.2(平均值-39.8;ΔFMQ=-5.7)和-41.8～-38.4之间(平均值-40.0;ΔFMQ=-5.5),对应的Log f_(S_2)在-14.9～-12.1(平均值-13.5)和-14.5～-12.7之间(平均值-13.6)。不同蚀变阶段矿物组合特征及热力学模拟结果表明,在早期高温的钾硅酸盐化阶段含矿流体具有高氧逸度、中性特征(ΔFMQ=2,pH=7),在中温青磐岩化阶段具有低氧逸度、酸性特征(ΔFMQ=0,pH=4.8),在晚期绢英岩化阶段pH值变化不大而氧逸度略有升高。综合上述矿化-蚀变时空结构和热力学模拟结果,本研究显示普朗铜矿床强烈的蚀变叠加与青磐岩化矿化现象与围岩碳质地层随着大气水沿断裂带渗入到岩浆热液系统中有关。还原性物质伴随着大气水的渗入破坏了原始岩浆热液系统化学平衡,可能是导致普朗铜矿蚀变叠加及在青磐岩化阶段铜等成矿物质大规模聚集的关键原因之一。     

Cu diffusivity in granitic melts with application to the formation of porphyry Cu deposits

We report new experimental data of Cu diffusivity in granite porphyry melts with 0.01 and 3.9 wt% H₂O at 0.15–1.0 GPa and 973–1523 K. A diffusion couple method was used for the nominally anhydrous granitic melt, whereas a Cu diffusion-in method using Pt₉₅Cu₅ as the source of Cu was applied to the hydrous granitic melt. The diffusion couple experiments also generate Cu diffusion-out profiles due to Cu loss to Pt capsule walls. Cu diffusivities were extracted from error function fits of the Cu concentration profiles measured by LA-ICP-MS. At 1 GPa, we obtain \({D_{{\text{Cu, dry, 1 GPa}}}}=\exp \left[ {( - {\text{13.89}} \pm {\text{0.42}}) - \frac{{{\text{12878}} \pm {\text{540}}}}{T}} \right],\) and \({D_{{\text{Cu, 3}}{\text{.9 wt\% }}{{\text{H}}_{\text{2}}}{\text{O}},{\text{ 1 GPa}}}}=\exp \left[ {( - 16.31 \pm 1.30) - \frac{{{\text{8148}} \pm {\text{1670}}}}{T}} \right],\) where D is Cu diffusivity in m²/s and T is temperature in K. The above expressions are in good agreement with a recent study on Cu diffusion in rhyolitic melt using the approach of Cu₂S dissolution. The observed pressure effect over 0.15–1.0 GPa can be described by an activation volume of 5.9 cm³/mol for Cu diffusion. Comparison of Cu diffusivity to alkali diffusivity and its variation with melt composition implies fourfold-coordinated Cu⁺ in silicate melts. Our experimental results indicate that in the formation of porphyry Cu deposits, the diffusive transport of magmatic Cu to sulfide liquids or fluid bubbles is highly efficient. The obtained Cu diffusivity data can also be used to assess whether equilibrium Cu partitioning can be reached within certain experimental durations.     

Exploration potential of Cu isotope fractionation in porphyry copper deposits

We examined the copper isotope ratio of primary high temperature Cu-sulfides, secondary low temperature Cu-sulfides (and Cu-oxides) as well as Fe-oxides in the leach cap, which represent the weathered remains of a spectrum of Cu mineralization, from nine porphyry copper deposits. Copper isotope ratios are reported as δ⁶⁵Cu‰ = ((⁶⁵Cu/⁶³Cu_sample/⁶⁵Cu/⁶³Cu_{NIST 976 standard}) − 1) ? 10³. Errors for all the analyses are ± 0.14‰ (determined by multiple analyses of the samples) and mass bias was corrected through standard-sample-standard bracketing. The overall isotopic variability measured in these samples range from − 16.96‰ to 9.98‰.     

中亚成矿域斑岩铜矿床基本特征

中亚成矿域发育许多大型和超大型斑岩铜矿床,是世界上重要的斑岩铜矿成矿域。我们对9个大型和超大型斑岩铜矿床进行了研究,包括地质特征、含矿岩体地球化学、SIMS锆石U-Pb定年和成矿流体成分等,结合前人成果,我们认为中亚成矿域斑岩铜矿床具有如下特点:(1)成矿时代为古生代和中生代,成矿高峰期为泥盆纪和石炭纪;(2)含矿岩浆为钙碱性中酸性岩浆和少量的碱性岩浆,含矿岩体为花岗闪长岩、闪长岩、英云闪长岩和少量的二长岩;(3)含矿岩浆大多数源于新生的洋壳,少量有古老的基底物质和围岩物质参与;(4)成矿构造背景主要为岛弧,少量为陆缘弧和岛弧向陆缘弧过渡的环境;(5)矿床可分为三类,包括斑岩型Cu-Au、Cu(Au,Mo)和Cu-Mo矿床;(6)成矿流体可分为两类,包括氧化性H2O-Na Cl-CO2-SO2体系和少量的还原性H2O-Na Cl-CH4-CO2体系;(7)成矿系统可分为三类,包括简单的斑岩系统和少量的斑岩-矽卡岩成矿系统和斑岩-浅成低温热液成矿系统。     

Chalcophile elemental compositions and origin of the Tuwu porphyry Cu deposit,NW China

The Tuwu porphyry Cu deposit in the eastern Tianshan Orogenic Belt of southern Central Oceanic Orogen Belt contains 557 Mt ores at an average grade of 0.58 wt.% Cu and 0.2 g/t Au, being the largest porphyry Cu deposit in NW China. The deposit is genetically related to dioritic and plagiogranitic porphyries that intruded the Carboniferous Qieshan Group. Ore minerals are dominantly chalcopyrite, pyrite and enargite. Porphyric diorites have Sr/Y and La/Yb_N ratios lower but Y and Yb contents higher than plagiogranites. Diorites have highly variable Cu but nearly constant PGE contents (most Pd = 0.50–1.98 ppb) with Cu/Pd ratios ranging from 10,900 to 8,900,000. Plagiogranites have PGEs that are positively correlated with Cu and have nearly uniform Cu/Pd ratios (5,100,000 to 7,800,000). Diorites have concentrations of Re (0.73–15.18 ppb), and ¹⁸⁷Re/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os ratios lower but common Os contents (0.006–0.097 ppb) higher than plagiogranites. However, both the diorites and plagiogranites have similar normalized patterns of rare earth elements (REE), trace element and platinum-group elements (PGEs). All the samples are characterized by the enrichments of LREE relative to HREE and display positive anomalies of Pb and Sr but negative anomalies of Nb and Ta in primitive-mantle normalized patterns. In the primitive mantle-normalized siderophile element diagrams, they are similarly depleted in all PGEs but slightly enriched in Au relative to Cu.Our new dataset suggests that both the diorite and plagiogranite porphyries were likely evolved from magmas derived from partial melting of a wet mantle wedge. Their parental magmas may have had different water contents and redox states, possibly due to different retaining time in staging magma chambers at the depth, and thus different histories of magma differentiation. Parental magmas of the diorite porphyries are relatively reduced with less water contents so that they have experienced sulfide saturation before fractional crystallization of silicate minerals, whereas the relatively more oxidized parental magmas with higher water contents of the plagiogranite porphyries did not reach sulfide saturation until the magmatic-hydrothermal stage. Our PGE data also indicates that the Cu mineralization in the Tuwu deposit involved an early stage with the enrichments of Au, Mo and Re and a late stage with the enrichment of As but depletion of Au–Mo. After the formation of the Cu mineralization, meteoric water heated by magmas penetrated into and interacted with porphyritic rocks at Tuwu, which was responsible for leaching Re from hosting rocks.     

A new linguistic quantifier knowledge-guided OWA approach for mineral prospectivity mapping: a case study of the Bavanat Region,Iran

The main purpose of this study is to introduce a geographic information system (GIS)-based, multi-criteria decision analysis method for selection of favourable environments for Besshi-type volcanic-hosted massive sulphide (VHMS) deposits. The approach integrates two multi-criteria decision methods (analytical hierarchy process and ordered weighted averaging) and theory of fuzzy sets, within a GIS environment, to solve the problem of big suggested areas and missing known ore deposits in favourable environment maps for time and cost reduction. We doubled the fuzzy linguistic variables’ significance as a method to apply the arrange weights that the analytical hierarchy process (AHP)-ordered weighted averaging (OWA) hybrid procedure depends on. Another aim of this work is to assist mineral deposit exploration by modelling existing uncertainty in decision-making. Both AHP and fuzzy logic methods are knowledge-based, and they are affected by decision maker judgments. We used data-driven OWA approach in a hybrid method for solving this problem. We applied a new knowledge-guided OWA approach on data with changing linguistic variables according to the mineral system for VHMS deposits. Additionally, we used a vector-based method combination, which increased the precision of results. Results of knowledge-guided OWA showed that all of the mines and discovered deposits have been predicted with 100% accuracy in half of the size of the suggested area. To summarize, results improved the selection of possible target sites and increased the accuracy of results as well as reducing the time and cost, which will be used for field exploration. Finally, the hybrid methods with a knowledge-guided OWA approach have delivered more reliable results compared to exclusively knowledge-driven or data-driven methods. The study proved that expert knowledge and processed data (information) are critical important keys to exploration, and both of them should be applied in hybrid methods for reaching reliable results in mineral prospectivity mapping.     

Adakite-like signature of porphyry granitoid stocks in the Meiduk and Parkam porphyry copper deposits,NE of Shahr-e-Babak,Kerman, Iran: Constrains on geochemistry

The Middle Miocene porphyry granitoid stocks of Meiduk and Parkam porphyry copper deposits are intruded in the north-western part of the Dehaj-Sarduiyeh volcano-sedimentary belt in the south-eastern extension of the Urumieh-Dukhtar Magmatic Arc (UDMA) in Iran. The porphyritic to microgranular granitoids are mainly consist of quartz diorite, granodiorite and diorite. The whole rock geochemical analyses of these rocks reveals sub-alkaline, calc-alkaline, meta-peraluminous and I-type characteristics. Their geochemical characteristics such as Al₂O₃ content of 13.51–17.05 wt%, high Sr concentration (mostly >400 ppm), low Yb (an average of 0.74 ppm) and Y (an average of 9.02 ppm) contents, strongly differentiated REE patterns (La/Yb ≥ 20), lack of Eu anomaly (Eu/Eu¹ ≥ 1) are indicative of adakitic signature. Their enrichment in low field strength elements (LFSE) and conspicuous negative anomalies for Nb, Ta and Ti are typical of subduction related magmas. Detailed petrological studies and geochemical data indicated that Meiduk and Parkam porphyry granitoids were derived from amphibole fractionation of hydrous melts at a depth of >40 km in a post-collisional tectonic setting.     

Gold Distribution in Pyrite of the Senjedeh Gold Deposit,Muteh Mining District, NW of Iran

Please refer to the attachment(s) for more details     

斑岩铜矿研究中若干问题探讨

文章从全球角度对斑岩铜矿的若干问题进行了评述,对斑岩铜矿的源区及岩浆岩特征、Mash带的地质意义、埃达克岩与斑岩铜矿的关系、过渡岩浆的地质意义、中国斑岩铜矿概况及斑岩铜矿的一般模式等问题进行了探讨。     

论新疆伊犁浅成低温热液型金矿与斑岩型铜（钼金）矿的相随相伴规律

中亚成矿域中的斑岩型铜（钼金）矿,有别于滨太平洋区的斑岩铜矿,它们大部分是形成于大洋消亡之后,与A型俯冲或后碰撞阶段的构造岩浆作用有关,并非都形成于岛弧发展阶段,且常与浅成低温热液型金矿（产于陆相-亚陆相火山岩内）时间相随、空间相伴,两者属于一个统一的岩浆系统;浅部是浅成低温热液型金矿,深部是高温斑岩型铜（钼金）矿,其成矿特点表现出两者元素组合连续、过渡与转化,两者类型相随相伴。     

Micrometallogeny and hydrothermal fluid evolution of the Iju porphyry Cu deposit,NW Kerman,Iran: Evidence from fluid inclusions,Laser Raman spectroscopy,and SO isotope systematics

The Iju Cu porphyry is located in the NW part of the Kerman Magmatic Copper Belt (KMCB). It is related to a ~ 9 Ma granodiorite porphyry intrusion, with three main stages of hydrothermal activity. The homogenization temperatures for the fluid inclusions are in the ranges of 200–494 °C, and their salinities vary from 4.0 to 42.8 wt% NaCl equiv., which are typical magmatic-hydrothermal fluids. The δ³⁴S values of sulfides range from −0.4 to +3.2 ‰ (V-CDT), and the δ³⁴S values of anhydrite samples range from +11.6 to +16.8 ‰. The δ³⁴S values of sulfides show a narrow range, implying a homogeneous sulfur source. The oxygen isotopic composition of hydrothermal water in equilibrium with quartz samples ranges from +3.4 to +6.0 ‰ (V-SMOW) consistent with the hydrothermal fluids having a magmatic signature, but diluted with meteoric waters in the main mineralizing stage. The most important factors responsible for metal precipitation in the Iju porphyry deposit are fluid boiling, oxygen fugacity decrease and cooling followed by dilution with meteoric water. The primary fluids of the Iju Cu deposit are characterized by relatively high temperature and moderate salinity, and are CO₂-rich, indicating a typical post-collisional porphyry system.     

特提斯成矿域中新世斑岩铜矿岩石成因、源区、构造演化及其成矿作用过程

作为全球三大成矿域之一,特提斯成矿域发育众多的世界级成矿带(矿床),例如,旁地德斯、萨汉德-巴兹曼、贾盖、玉龙、冈底斯成矿带等。为了进一步了解特提斯成矿域中新世斑岩铜矿的成因及成矿作用,本文对萨汉德-巴兹曼、贾盖和冈底斯铜矿带典型矿床的地质、地球化学、Sr-Nd-Pb数据进行对比分析,探讨含矿斑岩岩石成因、源区特征和构造环境,归纳其构造演化与其成矿作用过程。地球化学数据显示,这三个铜矿带中新世斑岩体总体显示钙碱性I型花岗岩的特征,具有埃达克岩亲和性。与冈底斯铜矿带相比较,萨汉德-巴兹曼铜矿带和贾盖铜矿带斑岩体显示出弧岩浆岩与埃达克岩过渡的地球化学特征,暗示其岩浆源区MORB质角闪榴辉岩或榴辉岩可能发生的较大程度的部分熔融。Sr-Nd-Pb同位素数据显示,这些含矿斑岩主要来源于受岩浆作用控制的壳幔混合物质,显示DUPAL异常。综合研究分析,认为这些含矿斑岩可能形成于岛弧造山带演化过程中,是洋壳俯冲消减和大陆碰撞过程中增厚下地壳部分熔融的结果。     

A synthesis of iron deposits in the eastern Tianshan,NW China

The northern Xinjiang region is one of the most significant iron metallogenic provinces in China.Iron deposits are found mainly within three regions:the Altay,western Tianshan,and eastern Tianshan orogenic belts.Previous studies have elaborated on the genesis of Fe deposits in the Altay orogenic belt and western Tianshan.However,the geological characteristics and mineralization history of iron deposits in the eastern Tianshan are still poorly understood.In this paper I describe the geological characteristics of iron deposits in the eastern Tianshan,and discuss their genetic types as well as metallogenic-tectonic settings,Iron deposits are preferentially distributed in central and southern parts of the eastern Tianshan.The known iron deposits in the eastern Tianshan show characteristics of magmatic Fe-Ti-V(e.g.,Weiya and Niumaoquan),sedimentary-metamorphic type(e.g.,Tianhu),and iron skarn(e.g.,Hongyuntan).In addition to the abovementioned iron deposits,many iron deposits in the eastern Tianshan are hosted in submarine volcanic rocks with well-developed skarn mineral assemblages.Their geological characteristics and magnetite compositions suggest that they may belong to distal skarns.SIMS zircon U-Pb analyses suggest that the Fe-Ti oxide ores from Niumaoquan and Weiya deposits were formed at 307.7±1.3 Ma and 242.7±1.9 Ma,respectively.Combined with available isotopic age data,the timing of Fe mineralization in the eastern Tianshan can be divided into four broad intervals:Early Ordovician-Early Silurian(476-438 Ma),Carboniferous(335-303 Ma),Early Permian(295-282 Ma),and Triassic(ca.243 Ma).Each of these episodes corresponds to a period of subduction,post-collision,and intraplate tectonics during the Paleozoic and Mesozoic time.     

Carboniferous porphyry Cu (-Au) mineralization of the West Junggar region,NW China: the Shiwu example

ABSTRACT

The West Junggar region, located in the Central Asian Orogenic Belt (CAOB), is characterized by extensive Carboniferous magmatism and porphyry Cu (-Au) deposits. The Shiwu porphyry Cu-Au deposit, located in the east of the Barluk Mountains, the West Junggar region, is not only a newly discovered deposit but also a representative porphyry Cu-Au deposit in this area. The volcanic rocks (including andesite and tuff) and intrusive rocks (including diorite, quartz diorite, quartz diorite porphyry, and tonalite porphyry) occurred in the Shiwu area and the mineralization associated with the quartz diorite porphyry. The secondary ion mass spectrometry (SIMS) zircon U–Pb ages of quartz diorite porphyry and tonalite porphyry are 310.4 ± 2.3 Ma and 310.1 ± 2.4 Ma, respectively, indicating that the Shiwu deposit is related to the Late Carboniferous magmatism. Intrusive rocks, which were characterized by the enrichment of large ion lithophile elements (LILEs) and pronounced negative high field strength elements (HFSEs), belong to the calc-alkaline or tholeiitic series. Their (⁸⁷Sr/⁸⁶Sr)_i, (¹⁴³Nd/¹⁴⁴Nd)_I, and εNd(t) values range from 0.703569 to 0.704311, 0.512488 to 0.512512, and 4.9 to 5.3, respectively. Volcanic rocks, which belong to the calc-alkaline series, have similar geochemical features as the intrusive rocks, and their (⁸⁷Sr/⁸⁶Sr)_i, (¹⁴³Nd/¹⁴⁴Nd)_i, and εNd(t) values, respectively, are 0.703704–0.704071, 0.512520–0.512542, and 5.49–5.92. These characters indicate that the igneous rocks in the Shiwu area derived dominantly from the mantle and formed in an island arc setting. These characters also further confirmed that the Barluk Mountains is still in an island arc setting in the Late Carboniferous and the accretionary orogenesis can exist until 310 Ma at least.     

Recycling of orogenic arc crust triggers porphyry Cu mineralization in Kerman Cenozoic arc rocks,southeastern Iran

Pre-collisional Eocene–Oligocene arc diorites, quartzdiorites, granodiorites, and volcanic equivalents in the Kerman arc segment in central Iran lack porphyry Cu mineralization and ore deposits, whereas collisional middle-late Miocene adakite-like porphyritic granodiorites without volcanic equivalents host some of the world’s largest Cu ore deposits. Petrological and structural constraints suggest a direct link between orogenic arc crust evolution and the presence of a fertile metallogenic environment. Ore-hosting Kuh Panj porphyry intrusions exhibit high Sr (>400 ppm), low Y (<12 ppm) contents, significant REE fractionation (La/Yb > 20), no negative Eu anomalies (Eu/Eu^* ≥ 1), and relatively non-radiogenic Sr isotope signatures (⁸⁷Sr/⁸⁶Sr = 0.7042–0.7047), relative to Eocene–Oligocene granitoids (mainly Sr < 400 ppm; Y > 12; La/Yb < 15; Eu/Eu^* < 1; ⁸⁷Sr/⁸⁶Sr = 0.7053–0.7068). Trace element modeling indicates peridotite melting for the barren Eocene–Oligocene intrusions and a hydrous garnet-bearing amphibolite source for middle-late Miocene ore-hosting intrusions. The presence of garnet implies collisional arc crustal thickening by shortening and basaltic underplating from about 30–35 to 40–45 km or 12 kbar. The changes in residual mineralogy in the source of Eocene to Miocene rocks in the Kerman arc segment reflect probing of a thickening arc crust by recycling melting of the arc crustal keel. Underplating of Cu and sulfur-rich melts from fertile peridotite generated a fertile metallogenic reservoir at or near the crust–mantle boundary, and dehydration melting under oxidizing conditions produced syn- and post-collisional ore-hosting intrusions, while the lack of post-collisional volcanism prevented the venting of volatiles to the atmosphere from sulfur-rich and oxidized adakitic magmas. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.