Orogenic Gold Mineralization in the Qolqoleh Deposit, Northwestern Iran

The Qolqoleh gold deposit is located in the northwestern part of the Sanandai‐Sirjan Zone, northwest of Iran. Gold mineralization in the Qolqoleh deposit is almost entirely confined to a series of steeply dipping ductile–brittle shear zones generated during Late Cretaceous–Tertiary continental collision between the Afro‐Arabian and the Iranian microcontinent. The host rocks are Mesozoic volcano‐sedimentary sequences consisting of felsic to mafic metavolcanics, which are metamorphosed to greenschist facies, sericite and chlorite schists. The gold orebodies were found within strong ductile deformation to late brittle deformation. Ore‐controlling structure is NE–SW‐trending oblique thrust with vergence toward south ductile–brittle shear zone. The highly strained host rocks show a combination of mylonitic and cataclastic microstructures, including crystal–plastic deformation and grain size reduction by recrystalization of quartz and mica. The gold orebodies are composed of Au‐bearing highly deformed and altered mylonitic host rocks and cross‐cutting Au‐ and sulfide‐bearing quartz veins. Approximately half of the mineralization is in the form of dissemination in the mylonite and the remainder was clearly emplaced as a result of brittle deformation in quartz–sulfide microfractures, microveins and veins. Only low volumes of gold concentration was introduced during ductile deformation, whereas, during the evident brittle deformation phase, competence contrasts allowed fracturing to focus on the quartz–sericite domain boundaries of the mylonitic foliation, thus permitting the introduction of auriferous fluid to create disseminated and cross‐cutting Au‐quartz veins. According to mineral assemblages and alteration intensity, hydrothermal alteration could be divided into three zones: silicification and sulfidation zone (major ore body); sericite and carbonate alteration zone; and sericite–chlorite alteration zone that may be taken to imply wall‐rock interaction with near neutral fluids (pH 5–6). Silicified and sulfide alteration zone is observed in the inner parts of alteration zones. High gold grades belong to silicified highly deformed mylonitic and ultramylonitic domains and silicified sulfide‐bearing microveins. Based on paragenetic relationships, three main stages of mineralization are recognized in the Qolqoleh gold deposit. Stage I encompasses deposition of large volumes of milky quartz and pyrite. Stage II includes gray and buck quartz, pyrite and minor calcite, sphalerite, subordinate chalcopyrite and gold ores. Stage III consists of comb quartz and calcite, magnetite, sphalerite, chalcopyrite, arsenopyrite, pyrrhotite and gold ores. Studies on regional geology, ore geology and ore‐forming stages have proved that the Qolqoleh deposit was formed in the compression–extension stage during the Late Cretaceous–Tertiary continental collision in a ductile–brittle shear zone, and is characterized by orogenic gold deposits.     

Early Cretaceous sedimentary provenance and structural evolution of the central Sanandaj–Sirjan Zone,Iran: implications for palaeogeographic reconstructions of the northern Neo-Tethyan margin

ABSTRACT

The Early Cretaceous was an important epoch in the evolution of the Earth system in which major tectonic episodes occurred, especially along the Alpine–Himalayan belt. The paucity of reliable palaeogeographic data from the central segment of this geological puzzle, however, hampers the reconstruction of a panoramic view of its Early Cretaceous palaeogeography and geodynamic setting. Here we present multidisciplinary provenance data from Lower Cretaceous strata of the overriding plate of the Neo-Tethyan subduction zone (the Sanandaj–Sirjan Zone; SSZ, of central Iran), including structural, basin-fill evolution, petrographic and geochemical analyses. Sandstone provenance analysis of Lower Cretaceous red beds suggests the occurrence of sub-mature litho-quartzose sandstones attributed to an active continental arc margin in convergent setting predominantly derived from plutonic, quartzose sedimentary and metamorphic rocks exposed in the central SSZ. Weathering indices indicate moderate chemical weathering in the source area which may be related to close source-to-sink relationships or arid climate. Our palaeogeographic reconstructions and original geological mapping indicate that the erosion of uplifted basement rocks exposed in horst blocks provided the sediment sources for the syn-extensional deposition of uppermost Jurassic–lowermost Cretaceous conglomerates and Lower Cretaceous siliciclastic red beds within a continental retro-arc basin during initiation of the ‘Neo-Tethys 2?. The polyphase tectonic reactivation along the principal fault of the study area controlled the syn- and post-extensional tectonostratigraphic evolution that reflect the corresponding mechanical decoupling/coupling along the northern Neo-Tethyan plate margin.     

Tectonic elements controlling the evolution of the Gulf of Saros (northeastern Aegean Sea, Turkey)

Tectonic elements controlling the evolution of the Gulf of Saros have been studied based upon the high-resolution shallow seismic data integrated with the geological field observations. Evolution of the Gulf of Saros started in the Middle to Late Miocene due to the NW–SE compression caused by the counterclockwise movement of the Thrace and Biga peninsulas along the Thrace Fault Zone. Hence, the North Anatolian Fault Zone is not an active structural element responsible for the starting of the evolution of the Gulf of Saros. The compression caused by the rotational movement was compensated by tectonic escape along the pre-existing Ganos Fault System. Two most significant controllers of this deformation are the sinistral Ganos Fault and the dextral northern Saros Fault Zone both extending along the Gulf of Saros. The most important evidences of this movement are the left- and right-oriented shear deformations, which are correlated with structural elements, observed on the land and on the high-resolution shallow seismic records at the sea. Another important line of evidence supporting the evolution of this deformation is that the transgression started in the early-Late Miocene and turned, as a result of regional uplift, into a regression on the Gelibolu Peninsula during the Turolian and in the north of the Saros Trough during the Early Pliocene. The deformation on the Gelibolu Peninsula continued effectively until the Pleistocene. Taking into account the fact that this deformation affected the Late Pleistocene units of the Marmara Formation, the graben formation of the Gulf of Saros is interpreted as a Recent event. However, at least a small amount of compression on the Gelibolu Peninsula is observed. It is also evident that compression ceased at the northern shelf area of the Gulf of Saros.     

The role of the border city Hunchun on Tumen River, China

Since the Tumen River Area Development Project(TRADP) was launched in 1991, Hunchun city located between North Korea and Russia along the river corridor, has become an important and unique border city. Hunchun, formerly a strategic military city, is emerging as an international trade linkage center through Satouz and Quanhe on the North Korea side and through Changlinzi on the Russian side. Furthermore, the establishment and operation of the Hunchun Border Economic Cooperation Zone (HBECZ) in the city is becoming the main source of the growth, providing a new role for the border city. Its underlying economic momentum comes from the combination of the Chinese-Korean labor force and foreign investment and technology transferred from Korea, Japan, and others. The most important expected new role for Hunchun is as a new 21st century entrepot connection between the Pacific rim and Eurasia by rail and trunk lines, and as a new regional center of the border region based on both a newly generated urban subsystem and the increasing informal sector of cross border business. However, there are many obstacles to overcome in the near future, such as the possible military tensions among the three border nations, the guarantee of free entries and sailing on the Tumen river, and agreements concerning environmental conservation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Country‐rock structural fabrics as a guide to pluton emplacement depth: An example from the Hodgkinson Province,northeastern Australia

Country‐rock structures adjacent to plutons of the linear, northwest‐southeast‐trending Mt Alto Supersuite, Hodgkinson Province, northeastern Australia, are variably developed from north to south along the belt. S₃ and S₄ cleavages show close temporal relationships with pluton emplacement and are better and more widely developed around plutons in the north, whereas much weaker cleavages of the same generation are only sporadically developed to the south. Cleavage trend lines anastomose around less elongate plutons to the north but are generally truncated by more elongate plutons to the south. It is proposed that a major crustal dislocation, the Alto Fault Zone, comprises a set of subparallel structures that formed prior to granite intrusion and controlled emplacement of some plutons and their final shapes. The north‐south variation in structural relations is interpreted to reflect a corresponding variation in depth of emplacement from north to south, which resulted when post‐emplacement reactivation of the Alto Fault Zone uplifted and sinistrally displaced the northern end of the supersuite relative to the southern end. Reactivation of the fault zone after granite emplacement is supported by the truncation of some plutons.     

云南东川新山含金剪切带型金矿

新山金矿属构造剪切带控制的典型金矿床,产于中元古界昆阳群美党组(Pt2m)中部变质石英砂板岩中。规模大、品位富、易采易选。矿区构造——含金剪切带与土壤地球化学金异常,是寻找该类金矿的重要标志。     

云南孟连芒信金矿成因探讨

芒信金矿脉状、透镜状、串球状金矿体,赋存于石炭系碳酸盐岩破碎带中。以裂隙金、晶隙金、固溶金、吸附金状存在。经历沉积—变质—岩浆活动等阶段。     

潞西团坡厂铁锌多金属矿成因

矿体产于印支期黑云角闪花岗闪长岩与寒武系(未分,∈?)变质岩接触带,F1压扭性断裂控制矿体的形态和展布。成因类型为热液接触交代一矽卡岩型铁锌矿。     

云南昌宁文沧铜矿矿床特征及找矿思路

矿体产于平掌组变质绿片岩中,NW向F3断裂破碎带控矿。边缘向中央品位增高。研究构造延伸和矿源可扩大远景。     

江苏东海地区石英脉地质特征及找矿方向

区域变质作用、韧性剪切作用和超高压变质作用为SiO2富集创造条件,印支期-燕山期的构造活动为石英脉富集定位创造构造环境。东海群地层、韧性剪切带、超高压变质带为石英脉的形成提供了SiO2物质来源。