Baode Wang

Study on the Metallogenetism of Sub-mantle Plume and Mantle Branches in the Gold Mineralization Concentration Area of Northwest Jiaodong Peninsula

The northwest of Jiaodong peninsula is characterized by its greatest gold concentration area, enormous gold reserves and limited time interval(115±5Ma) of gold mineralization in China. Studies show that the east area of north China began its mantle plume evolution since the Yanshanian movement, and the Laiyang sub-mantle plume and its surrounding mantle branches such as those in Guojiadian, Aishan and Panshidian were formed in the mineralization concentration area of northwestern Jiaodong peninsula. With the development of mantle plume → sub-mantle plume → mantle branch → favorable expending structures, the deep-derived hydrothermal fluid moved up to the favorable places, such as brittle-ductile or ductile-brittle shearing zones, the internal and external contact zones of intrusions, dense fracturing zones and the contact zones between dikes and countryrocks, and concentrated into deposits. Then the gold mineralization concentration zones that are centralized on mantle branches were formed. This study takes Guojiadian mantle branch as an example to discuss their metallogenetism and conclude the metallogenetic mode.

Study on the ore-forming and ore-controlling structure of the Mujicun Cu (Mo) ore deposit, Hebei Province, China

The Mujicun Cu (Mo) ore deposit at Laiyuan, Hebei Province, is a currently proven large-sized Cu (Mo) polymetallic ore deposit and it is located in the second-ordered fault depression basin of the ditachment belt on the hanging-wall on the western side at the juncture of the Laiyuan dumbell-shaped complex in the northern part of the Fuping mantle-branch structure. Metallogenesis is controlled by diorite porphyrite in intrusive relation with the fault depression basin and other relevant fault structure systems and intenstive wall-rock alteration zones. This study, in conjunction with the most recent exploration data, analyzed the geological background of metallogenesis of this deposit, summaried the geological characteristics of typical ore deposits, determined the alteration zonation of the deposit, investigated regional metallogenesis and the genesis of typical ore deposits, discussed the regional ore-forming and ore-controlling structures, and generalized the regional ore-controlling model and metallogenic model of the deposit. It is considered that the Mujicun porphry Cu (Mo) deposit, the Tieling, Futuyu, Xiaoligou and other skarn-type Fe-Cu deposits and the He’ergou hydrothermal-type Pb-Zn-Ag deposit jointly constitute a three-in-one polymetallic orefield, with the characteristics of typical metallogenic series.

Analysis of the ore-controlling role of Guojiadian mantle branch structure, Northwest Shandong Peninsula, China

Metallogenesis in the gold ore-concentrated zone of Northwest Shandong Peninsula is closely related to deep processes. The region in the eastern part of North China entered into the stage of mantle plume evolution during the Yanshanian movement, following the long-time stage of stable platform evolution during Paleozoic time. At that time, the ore-concentrated zone of Northwest Shandong Peninsula just entered into the development-evolution stage of the Laiyang sub-mantle plume and the Guojiadian mantle branch structure in its periphery. The core-mantle-source gold was present in the gas-liquid form, and it migrated through mantle plume→sub-mantle plume→mantle branch structure→favorable tectonic expansion zone to the favorable loci of the mantle branch structure, where gold was deposited as ores, thereafter constituting a series of large- to medium-sized gold deposits distributed around the Guojiadian mantle branch structure. This study also dealt with the Jiaojia fault as the main detachment (fault altered rock) belt on the northwestern margin of the mantle branch structure and also presented a basic cognition about the fact that the Sanshandao fault as the listric fault on the hanging wall of the detachment belt. Furthermore, on this basis, this study also pointed out the orientation for further ore prospecting in this region.

Isotope tracers for deep-seated fluids and noble gases

The role of He and Ar isotopes in tracing the source of ore fluids has aroused great attention of the broad masses of the geological researchers. On the basis of lots of test and measurement of He and Ar isotopes in sulfides from Au, Ag polymetallic ore deposits in northern China, statistics has been made on the published He and Ar isotope data from 27 gold deposits, 13 silver polymetallic ore deposits, 8 polymetallic ore deposits, 1 rare-earth deposit, 3 oceanic incrustations, 3 volcanic springs and their wall rocks and granites. The statistical results indicate that the 3He/4Ar (×10−6) values of the Au, Ag polymetallic ore deposits are within the range of 0.24–9.39, with an average of 3.34×10−6; the He/Ar values, 0.007–6.01,with an average of 2.37; the 40Ar/36Ar values, 265.75–2361, with an average of 699.0; the 4He/40Ar values, 0.0020–643.86, with an average of 5.85, the 3He/4Ar (×10−6) values of gneiss and granite surrounding the mining area, 0.001–1.79, with an average of 1.00×10−6, reflecting great differences in source. Mantle-source He in 48 Au, Ag polymetallic ore deposits accounts for 4.55%–83.06%, averaging 29.91%. It falls near the mantle-source region which can be seen in the He isotopic concentration diagram and the 3He/4He(R/Ra)-40Ar/36Ar plot. Studies suggested that the ore-forming materials for endogenic Au, Ag polymetallic ore deposits should be derived from the deep interior of the Earth, and with the multi-stage evolution of mantle plumes the deep-seated ore fluids would be transported from the deep interior of the Earth to the shallow levels. During this process the mixing of crust/mantle-source fluids would inevitably occur, therefore, the value range always lies between the mantle and the crust.

Source of fluids in the Longquanzhan gold deposits in the Yishui area, Shandong, China

The Longquanzhan gold deposit, hosted in Archean gneiss is located along the Tanlu fault zone, on the southeastern margin of the North China craton. The orebodies occur as veins striking 15°–18° and dipping SE at 35°–62°. Wall rock alteration types include silicification, pyritization, and sericitization, and chloritization, calcitization. Metallic minerals in ores are dominated by pyrite. Gold occurs mainly in the form of electrum. All inclusions are two-phase (L+V) NaCl- H2O type. The inclusions generally range in diameter from 2 to 8 µm with a vapour/liquid ratio of 5–90% and mainly 5–10%. The homogenization temperatures of fluid inclusions in the Longquanzhan gold deposit are between 108 and 300°C. The ice-melting temperatures vary from −2.0 to −8.6°C, at a peak of −2.5 to −7.0°C. The salinities determined from the ice-melting point of the fluid inclusions range from 3.39 to 12.39 wt.% NaCl equiv. According to isotope fractionation equation and mean homogenization temperatures, the δ18O values of the mineralizing fluids are calculated, ranging from −0.28‰ to +4.07‰, showing mixing of oreformi fluids and meteoric waters. The 3He/4He ratios of fluid inclusions in pyrite are 0.14–0.24 Ra, suggesting the crustal source of ore-forming fluid. The assemblage of alteration minerals, the characteristics of fluid inclusions and stable isotopes indicate that the Longquanzhan gold deposit belongs to epithermal type deposit.

The formation of a mantle-branch structure in western Shandong and its constraints on gold mineralization

On the basis of regional strata, magmatic activity, ring and radial faults, gently dipping detachments, geophysical information and isotopic age, this paper discusses the characteristics of mantlebranch structure in western Shandong. According to the characteristics of ore-control structures, gold deposits in the Luxi mantlebranch structure are divided into ductile shear zone type and detachment-slip layer type deposits. The detachment-slip layers type deposit, including the Guilaizhuang gold deposit and Mofanggou gold deposit are significant economic types. The_δ34S values of pyrite associated with gold mineralization exhibit a narrow range of-0.71 to 2.99%., implying that the sulfur was probably derived from the mantle or magma, whereas the_´18Ofluid and_´D values suggest that the ore-forming fluids of the gold deposits mixed with meteoric water in the shallow level.