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The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are mainly hosted in schist from the Gaixian Formation of the Liaohe Group. A detailed field geological survey showed that the quartz-vein type gold ore bodies are distributed in the near EW-trending and occur in the extensional tectonic space of schist in the Gaixian Formation, and the altered-rock type gold ore bodies are distributed in the near EW-trending structural belt and occur near in the Gaixian Formation of biotite schist, biotite granulite, marble and the upper footwall of dike. To further elucidate the source of ore-forming fluid and material in the Baiyun gold deposit, the H-O isotopes for quartz, S and Pb isotopes, in-situ trace elements for sulfides from quartz-vein and altered-rock type mineralization were studied. The H-O isotopic δDV-SMOW and δ18OH2O values of the auriferous quartz range were from −88.8‰ to −82.2‰ and −1.95‰ to 4.85‰, respectively, suggests that the ore-forming fluids were mainly magmatic water with minor meteoric water. The distribution ranges of in-situ S isotopic compositions of Au-bearing pyrite in the quartz-vein type and altered-rock type ores were −8.38‰–−10.47‰ (with average values of −7.89‰) and 11.38‰–17.52‰ (with average values of 11.55‰), respectively, indicating that the S isotopic compositions of the two ore types were clearly different. The in-situ Pb isotopic ratios changed almost uniformly, which showed that they had the same lead isotopic source. Based on the analysis of S and Pb isotopic compositions, the metallogenic materials in the Baiyun gold deposit were primarily from deep magma, and some wall rock materials may have been mixed in the metallogenic process. Co/Ni diagram shows that most Au-bearing pyrites have magmatic-hydrothermal or sedimentary alteration properties, and Au/As ratios were between 0.001 and 0.828 (the average value was 0.07), indicating that the ore-forming fluid in the Baiyun gold deposit may have been deep magma. Combining the geological, trace element, and isotopic data, as well as data from previous studies, we propose that the Baiyun gold deposit is a magmatic-hydrothermal ore deposit. [ABSTRACT FROM AUTHOR]

The Jiaodong Peninsula is one of the most important Au ore provinces in China. There is an ongoing debate on the correlation between ore formation and magmatism in this province, because few intrusive rocks exhibit a clear association with ore deposits. A mineralized biotite monzodiorite (BM) stock, with disseminated ore, pervasive phyllic alteration, and no deformation, was found in a borehole in the footwall of the Zhaoping fault within the Luanjiahe Au deposit, which may shed light on this debate. The biotite monzodiorite contains explosion breccias, miarolitic cavities, skeletal and dendritic quartz, and late-stage evolved aplite dikes, and the in-situ δ34S values of the disseminated pyrite which is associated with Au mineralization are −1.7‰ to 7.3‰ (mean=3.5‰), indicative of a magmatic-hydrothermal system. These findings, combined with the reported age of 123 Ma, show that the intrusion has close spatial, temporal, and geochemical relationships with Au mineralization in the area. The biotite monzodiorite is metaluminous, high-K calc-alkaline and shoshonitic, with enrichment in light rare earth elements (REEs) and large-ion lithophile elements (LILEs), depletion in high-field-strength elements (HFSEs), and enriched Sr-Nd isotopic compositions. The intrusion may be the product of partial melting of enriched lithospheric mantle with a small lower crustal component. The hydrous, Au-bearing, enriched mantle source, and the strongly oxidized magma that was generated, created favorable conditions for Au mineralization. [ABSTRACT FROM AUTHOR]

The Au value of stream sediments in swamp-forest areas in Northeast China is lower than in other areas, according to results from the Regional Geochemistry–National Reconnaissance Program. Two dissolution methods for measurement of Au levels were compared in this study. The Au values in samples dissolved by using four acids (HClO4 + HF + HNO3 + HCl) are larger than those dissolved by using aqua regia, especially when the Au content is greater than 1.25 ng/g. We found that a large amount of Au may be absorbed to or/and included in SiO2 colloids, apart from that occurring in organically bound forms in organic-rich sediments of swamp-forest areas. The Au absorbed to or/and included in SiO2 colloids is related to plant metabolism. This Au can migrate for long distances protected by high-concentration organic acids in water solution, but cannot be dissolved by aqua regia. The results of a pilot survey with an ultra-low sampling density in the Jiayin area, Heilongjiang Province, show that the Au anomalies obtained by using four-acid dissolution are not only larger in scale but also more coincident with corresponding metallogenic belts than those using aqua regia dissolution. [ABSTRACT FROM AUTHOR]

The Baoshan Block is tectonically located in the middle segment of the Sibumasu plate. Granitic magmatism within the Baoshan Block has been considered weakly active due mainly to very limited exposures during the Himalaya orogenic episode. The geochronological study on the buried Shuangmaidi granite has confirmed the existence of the Cenozoic granitoids in the Baoshan Block. The present study indicates that: (1) It is medium- to coarse-grained two mica phyric granite, characterized by high SiO (73.55%-77.16%) and low CaO (0.34%-1.38%) contents, with a total alkalis (KO+NaO) of 5.22%-8.03%, KO/NaO ratios of 0.24-1.79, and total rare earth elements (ΣREE) of the granite between 85 and 125 ppb. All samples are enriched in light REE and exhibit medium negative Eu anomalies; and they show pronounced negative anomalies in Ba, Sr, Ti, and Nb but significant positive anomalies in K, Rb, U, Th, and Pb on mantle-normalized trace element patterns, indicating typically peraluminous to strongly peraluminous S-type granite. (2) The zircon SHRIMP U-Pb ages of the granite are 36.27±0.48 Ma for the samples from ZK7-1 and 35.78±0.49 Ma for those from ZK0-1, respectively. The similar zircon ages from these two drill cores may suggest that the granite samples come from the same buried pluton. (3) Pb/Pb values of the granite vary from 20.115 to 25.359, Pb/Pb from 15.776 to 16.160, and Pb/Pb from 39.236 to 41.285, showing the characteristics of radioactive lead anomaly of the upper crust. The (Sr/Sr) values calculated on the average age of the two-mica orthoclase granite (36 Ma) range from 0.72524 to 0.77503 and ɛ( t) values vary from −10.9 to −11.7. These data, along with the depleted-mantle Nd modal ages of 1.73-1.80 Ga, imply that the granites might have formed from partial melting of the Precambrian crystal basements. (4) On the Hf-Rb-Ta diagram, almost all the samples fall within the field of post-collision tectonic setting. The CaO/NaO and AlO/TiO ratios suggest that the granitic magma may have formed from partial melting of clay-rich crustal materials with a possible melting temperature of about 900°C and a possible crystallization temperature of 775-795°C. (5) During the post-collision of the Himalaya orogen, with the southeastward extrusion of the Indochina continent resulting from the continuous northward indentation of the India continent into the Asia, the Gaoligong Fault, as the western boundary of the Indochina continent, moved in the dextral strike-slip on a large scale to trigger partial melting of the thickened crust, and the peraluminous granitic magma from which the Shuangmaidi two-mica orthoclase granite derived was formed. [ABSTRACT FROM AUTHOR]