Yan-Jing Chen

Origin of gold metallogeny and sources of ore-forming fluids, Jiaodong Province, eastern China

In this paper we use published isotopic ages for gold deposits and related rocks in the Jiaodong Peninsula (East Shandong Province) to investigate the origin of the large-scale gold metallogeny in the region, which contains world-class lode gold deposits. According to this database, metallogenic processes in this area occurred in the Mesozoic, with peak activities between 110 Ma and 130 Ma. In the Jiaodong gold province (JGP), the mineralizing events are coeval with or postdate Mesozoic granitoid intrusions. Both the Rb-Sr isochron ages and zircon SHRIMP age dating results suggest that Mesozoic granitoids were emplaced during several thermal events. The identification of inherited zircons coupled with ISr ratios (>0.709) indicate that these granitoids were mainly sourced from the continental crust, by remelting or partial melting. I Sr values obtained from ores and fluid inclusions are generally higher than 0.709, and slightly higher than those for Mesozoic granitoids. This also indicates that both ore fluids and metals were mainly sourced from the crust. Synthesis of the available data suggests that collision between the South and North China continents was probably the dominant factor responsible for the gold metallogeny in the JGP. Granitoid emplacement and large-scale gold metallogenesis can be related to three important stages in the geodynamic evolution of a collisional orogen (compression—crustal thickening—uplift, lithospheric delamination and transition to extension, and a final extension phase). The most important metallogenic phase occurred at the transition from collisional compression to extension tectonics.

Fluid inclusion study of the Tangjiaping Mo deposit, Dabie Shan, Henan Province: implications for the nature of the porphyry systems of post-collisional tectonic settings

The Tangjiaping porphyry Mo deposit in Shangcheng County is located in the Dabie continental collisional orogenic belt. The hydrothermal alteration and mineralization processes can be divided into three stages: K-feldspar + quartz + pyrite + magnetite + molybdenite in the early stage, quartz + pyrite + molybdenite ± chalcopyrite in the middle stage, and quartz + carbonate ± pyrite veins or carbonate veinlets in the late stage. The middle stage involved important Mo mineralization. Four compositional populations of fluid inclusions (FIs) occur in hydrothermal quartz formed in the early and middle stages, namely: pure CO2, CO2–H2O, daughter mineral-bearing, and NaCl–H2O. The late-stage quartz-carbonate ± pyrite veinlets contain only NaCl–H2O FIs. Homogenization temperatures of the early-stage FIs are mainly above 375°C, with salinities up to 62.10 wt.% NaCl equiv. Haematite daughter minerals, which probably represent an oxidizing environment, together with halite, sylvite, and chalcopyrite, are present in the FIs of this stage. Most of the middle-stage FIs homogenized between 235 and 335°C, with fluid salinities ranging from 1.06 to 45.87 wt.% NaCl equiv. In middle-stage quartz, besides halite and sylvite daughter minerals, abundant chalcopyrite and jamesonite are also present, reflecting a reducing environment. The daughter mineral-bearing FIs coexist with vapour- and liquid-rich FIs with contrasting salinities, and they homogenized in divergent ways at similar temperatures. This feature strongly suggests that fluid boiling occurred during the middle stage, which is well accepted as an important mechanism for the precipitation of ore-forming materials. FIs in late-stage minerals totally homogenized in the range 115–195°C, with low salinities ranging from 1.91 to 9.98 wt.% NaCl equiv. Combined with the published H–O isotope data, we propose that the initial ore fluids were magmatic in origin and were characterized by high temperature, high salinity, high oxygen fugacity, high levels of metallic elements, and high levels of CO2. In the middle stage, the fluids boiled and resulted in CO2 release, oxygen fugacity decrease, and rapid precipitation of ore-forming materials. The late-stage fluids, characterized by low temperatures, low salinities, and low contents of CO2, might have been sourced from meteoric water. Daughter mineral-bearing CO2–H2O FIs, especially multiple species daughter mineral-bearing FIs, are regarded as indicators of porphyry ore systems generated in continental collisional settings. This understanding is validated by recent studies of other porphyry ore systems in Chinese collision orogens.

Microstructure, interface and mechanical property of the DS NiAl/Cr(Mo,Hf) composite

A NiAl–Cr(Mo) composite containing Hf was directionally solidified under Ar atmosphere in Al2O3–SiO2 ceramic mold by the standard Bridgman method. The microstructure in the as-grown and hot isostatic pressing (HIP) conditions was studied using SEM, HREM and TEM equipped with EDXS. The composite was mainly composed of three phases, i.e. lamellar Cr(Mo), NiAl matrix and semi-continuously distributed Ni2AlHf. The common growth direction of NiAl and Cr(Mo) is , and the interface between them was atomically flat with no transition layer. Fine G-phase precipitates were formed in the presence of Si which was from the ceramic shell molds used during the directional solidification. The G-phase precipitates were cuboidal in shape and coherent with NiAl matrix. After the HIPed and aged treatment, the G-phase precipitates completely disappeared and the amount of intercellular Ni2AlHf phase was partially reduced. The mechanical properties were measured by tensile and compressive tests within the temperature range of 25∼1100°C. The BDTT of the HIPed and aged materials is significantly higher than the as-grown composite. The yield stress of the composite was higher than that of many NiAl-based alloys and possible strengthening mechanism were discussed.

METALLOGENIC GEODYNAMIC BACKGROUND OF MESOZOIC GOLD DEPOSITS IN GRANITE-GREENSTONE TERRAINS OF NORTH CHINA CRATON

The spatial distribution map of 65 mid-large gold-deposits hosted in the granite-greenstone terrains of the North China Craton is first drawn. These gold deposits mainly concentrate in the Mesozoic remobilized Yinshan-Yan-shan-Liaoning-Jilin intracontinental collisional orogenic belt, the northern Qinling and the Jiaodong Mesozoic collisional orogenic belts, and the Mesozoic intracontinental fault-magmatic belts developed along the Taihangshan and the Tan-Lu faults; their mineralizing time is predominantly Jurassic-Cretaceous, i. e. the Yanshanian. The metallogenic geodynamic background is exactly the compression-to-extension transition regime during continental collision.

Lead isotope systematics of the Weishancheng Au-Ag belt, Tongbai Mountains, central China: implication for ore genesis

The Weishancheng ore belt in the Tongbai Mountains consists of the Yindongpo large gold deposit, the Poshan and the Yindongling large silver deposits, and several other, smaller, ore deposits. All these ore deposits are stratabound within the Neoproterozoic Waitoushan Group, and are characterized by relative uniform lead isotope compositions: 206Pb/204Pb = 16.7529–17.2163, 207Pb/204Pb = 15.4166–15.6380, and 208Pb/204Pb = 38.2505–39.0500. These lead isotopic values are close to those of common lithologies of the Waitoushan Group, and quite different from other lithologic units or granitic batholiths in the Tongbai region. The lead isotope systematics of the Weishancheng ore belt suggests that the ores originated from the Waitoushan Group through metamorphic devolatilization. Based on the regional tectonic evolution, we propose that the ore-forming process occurred during the continental collision between the Yangtze and North China blocks; attendant metamorphic devolatilization of underthrust slabs induced the development of ore-forming fluids. Subsequently, intense water–rock interaction allowed the ore materials contained in the Waitoushan Group to be extracted, migrated, and enriched in the host carbonaceous sericite schist. We conclude that the Weishancheng Au-Ag ore belt can be classified as a stratabound, orogenic-style metallogenic system.

Metallogenesis of the Ertix gold belt, Xinjiang and its relationship to Central Asia-type orogenesis

The Ertix gold belt is located on the boundary of the Kalatongke arc and the Kelan back-arc basin of D-C1. Most scholars used to interpret the formation and distribution of the gold deposits in the Ertix tectonic belt in terms of the petrogenic and metallogenic models for active continental margins. However, enormous data of isotopic dating and geologic research show that the mineralization was obviously later than the oceanic subduction, whereas exactly simultaneous with the collisional orogenesis during C2-P, especially at the transition stage from collisional compression to extension. Based on study of metallogenic time, tectonic background, ore geology, ore fluid nature, ore material source, etc., we reveal that all the gold deposits possess the character of orogenic deposits formed in collisional orogenic system, and that their ore-forming materials mainly have derived from the stratigraphic terranes south to individual deposits. Accordingly, the theoretical tectonic model for collisional metallogenesis and petrogenesis is employed to explain the formation of the Ertix gold belt and to determine the gold exploration directions.

Progress and records in the study of endogenetic mineralization during collisional orogenesis

To develop and perfect the theory of plate tectonics and regional metallogeny, metallogenesis during collisional orogenesis should be thoroughly studied and will attract increasing attention of more and more scientists. This paper presents the main aspects of research and discussions on metallogenesis during collisional orogenesis after the development of plate tectonics, and accordingly divides the study history into two stages, i.e. the junior stage during 1971–1990 and the senior stage after 1990. Beginning with the negation of mineralization in the collision regime by Guild (1971), the focus of study was put on whether there occurred any mineralization during collisional orogenesis at the junior stage. At the senior stage, which is initiated by the advance of metallogenic and petrogenic model for collisional orogenesis, scientists begin to pay their attention to the geodynamic mechanism of metallogenesis, spatial and temporal distribution of ore deposits, ore-forming fluidization, relationship between petrogenesis and mineralization in collisional orogenesis, etc. Abundance of typical collisional orogens such as Himalayan, China has best natural conditions to study collisional metallogenesis. Great progress in the study of metallogenesis during collisional orogenesis has been made by Chinese geologists. Therefore, we hope that the’ Chinese geologists and Chinese governments at various levels to pay more attention to the study of collisional metallogenesis. Some urgent problems are suggested to be solved so as to bring about breakthroughs in the aspects concerned.

Hydrothermal ore systems associated with the extensional collapse of collision orogens

An integrated conceptual model explains the relationships between the geodynamic evolution of a collisional orogen and the development of hydrothermal ore systems. In this model magmatic activity and the generation of hydrothermal ore deposits in a collisional orogen reach a peak during the extensional collapse that follows asthenospheric mantle upwelling.

Isotope Geochemistry of the Weishancheng Stratabound Gold-Silver Ore Belt, Tongbai County, Henan Province, China

The Weishancheng ore belt is located in Tongbai Mountains and consists of three stratabound deposits (Yindongpo large gold deposit, Poshan super-large silver deposit, and Yindongling large silver-dominated poly-metallic deposit) and some small ore spots. The orebodies are strictly hosted in carbonaceous strata of the Neoproterozoic Waitoushan Formation. The H-O-C isotopic system of the fluid inclusions from each deposit indicates that the fluids in the early and middle ore-forming stages came from the metamorphic devolatilization, and in the late stage, considerable meteoric water entered the fluid system. The C-S-Pb isotope geochemistry suggests that the metallogenic materials are derived from the rocks from the Waitoushan Formation. The K-Ar and 40Ar-39Ar dating results show that the metallogenesis of the Weishancheng ore belt occurred during 100–140 Ma, when a tectonic setting changed from collisional compression to extension. The Weishancheng gold-silver ore belt belongs to a typical stratabound orogenic-type metallogenic system in terms of the ore-forming fluid, metal source, and geologic characteristics. The ore-forming process took place under the continental collision setting between Yangtze and North China plates.

The Great Oxidation Event and Its Records in North China Craton

In this chapter, we review the early Paleoproterozoic sedimentary records in North China Craton (NCC) and elsewhere in the world. We also propose a sequence framework for the subprime events happened in sedimentary sphere, biosphere, hydrosphere and atmosphere during the period of 2.5 to 1.8 Ga, and give an introduction to the Great Oxidation Event (GOE). These events are characteristic of the GOE, and are assigned to two main stages: (1) the early-stage hydrosphere oxidation (2.5–2.3 Ga), represented by the precipitation of the banded iron formations (BIFs), and (2) the late-stage atmospheric oxygenation (2.3–1.8 Ga), indicated by sediments of thick carbonate strata with 2.22–2.06-Ga δ13Ccarb positive excursion (Lomagundi Event), 2.25–1.95 Ga red beds, as well as the disappearance of BIFs at ca 1.8 Ga and prevail of black shales at 2.0–1.7 Ga. The 2.29–2.25-Ga Huronian Glaciation Event (HGE) demonstrated that the Earth’s superficial system oxidation had entered from hydrosphere into atmosphere. The 2.3-Ga turnpoint is a better Archean-Proterozoic boundary in Geological Time Chart.