LA-ICP-MS in situ analyses of the pyrites in Dongyang gold deposit,Southeast China:Implications to the gold mineralization

The Dongyang gold deposit is a newly discovered epithermal deposit in Fujian Province,Southeast China,along the Circum-Pacific metallogenic belt.Herewith,the authors present mineralogical,scanning electron microscope,and laser ablation inductively coupled clasma mass spectrometry analysis to reveal the relations between Au and Te,As,S,Fe,etc.,and discuss the gold precipitation process.The pyrites in this deposit are Fe-deficient,and are enriched in Te and As.The authors infer that As was mainly in form of As-complexes,and Te-Au-Ag inclusions/solid solution also exsits in the Py I.Along with the depletion of Te and As,they were less active chemically in the Py II,and Au may be incorporated into As-rich and Fe-deficient surface sites by chemisorption onto As-rich growth surfaces.Because of the incorporation of new fluid,Te and As became the most active chemically in the Py III,which was the main elements precipitation stage,and As dominantly substituted for S in the lattice of pyrite,due to the more reducing condition.The authors propose Au was in form of invisible gold,and the incorporation of gold can be considered as post-pyrite event,while the Au-bearing minerals were result of post incorporation of gold in arsenian pyrite.

Mineralogical Characteristics and its Prospecting Significance of Gold-Mercury Minerals in Davao Gold Placer in Mindanao Islands, Philippines

This paper has systematically researched mineral assemble and the characteristics of gold-mercury minerals in Davao Placer in Mindanao Islands, Philippines. The results show that reflection force of gold-mercury minerals has a strong-weak-strong of changes features as mercury＇s content in minerals increased. Otherwise their hardness of gold-mercury minerals reduced. While the hardness of gold-mercury minerals, which have isometric crystal structure, they are gradually become larger, the goldmalgam and r-Goldmalgamite just be found to exist as natural edge of gold-mercury mineral grains. Overall, mercury content is gradually reduced from the edge to the centre of gold-mercury minerals particles, but mercury-bearing in edge of the grains is lower than in the middle. Combination of the background of geological mineralization, this paper suggests that there are mantle-derived deposits such as Platinum, chromium in Philippines, which accompanied ultramafic-mafic magmation. It＇s most likely to found some large or extra large scale polymetallic deposits of gold and mercury, as well as coastal placers of gold, platinum, etc.

Trace Element Compositions of Pyrite from the Shuangwang Gold Breccias,Western Qinling Orogen,China:Implications for Deep Ore Prediction

The Shuangwang gold deposit, located in the Fengxian-Taibai fore-arc basin in the western Qinling Orogen of Central China, has yielded over 70 tons of gold. It is an orogenic gold deposit occurring in an NW-trending breccia belt. Most of the ores are hydrothermal breccia type containing fragments of adjacent strata cemented by ankerite and pyrite. Pyrite is the most abundant metallic mineral and the major gold-bearing mineral in the ores. A total of 58 pyrite samples from main ore bodies of the Shuangwang gold deposit have been analysed for 44 trace elements by HR-ICP-MS. Sb, Ba, Cu, Pb, Zn, Bi, Mo, Co are selected as indicator elements to investigate the potential usefulness of trace elements in pyrite as an indicator in gold exploration. The results show that the supra-ore halo elements Sb and Ba, which may have been more active than other near-ore halo elements and sub-ore halo elements, are best to characterize the shape of ore bodies. Five target areas are pointed out for deep ore exploration based on a comprehensive study of supra-ore, near-ore and sub-ore halos. This study provides evidence that trace elements in pyrite can be used to depict the deep extension of ore bodies and to vector towards undiscovered ore bodies.

Role of metasomatized mantle lithosphere in the formation of giant lode gold deposits:Insights from sulfur isotope and geochemistry of sulfides

The Wulong deposit is one of the largest quartz vein-type gold deposits with at least 80 tons of identified gold reserves in the eastern part of the Liaodong Peninsula.Gold orebodies are mainly hosted in the Late Jurassic gneissic two-mica granite and Early Cretaceous diorite dykes,and are structurally controlled by the NNE-and NW-trending faults.Gold mineralization mainly occurs as veins with lenticular shapes and is closely associated with sulfides and Bi minerals.Previous studies on the deposit mainly focused on its geological characteristics,fluid inclusions and the timing of gold mineralization.However,the extreme enrichment mechanism of gold,the geodynamic setting and ore source of the gold deposit remain equivocal.Here we present results from geochemical studies of pyrite and pyrrhotite at Wulong to address these issues.Pyrrhotite can be grouped into euhedral(Po1)and anhedral(Po2)varieties based on the textures.Four generations of pyrite were identified based on petrographic studies:Py1 is coarse-grained subhedral to euhedral crystal coexisting with milky quartz,and Au-depleted in composition;Py2 is represented by medium-grained,subhedral to anhedral pyrite coexisting with euhedral Po1,smoky quartz and minor chalcopyrite;Py3 occurs as fined-grained anhedral grains in the quartz-polymetallic sulfide veins;Py4 occurs as veinlets or aggregates in the quartz-calcite veins and contains the lowest Au concentrations.The time-resolved LA-ICP-MS ablation depth profiles of sulfides combined with detailed petrological observations indicate that gold mainly occurs either as invisible solid solution within the crystal lattice of sulfides,to some extent,or as small blebs of native gold and electrum.The close temporal and spatial relationships among native bismuth,native gold and Bi-Te-S minerals suggest that Bi-rich melts may have significantly sequestered gold from the hydrothermal fluids in the Wulong gold deposit.Sulfides from auriferous quartz veins have a restricted D33S range(-0.2‰to+0.2‰)and a mean d34S value of+1.25‰with a feature of the mass-dependent fractionation(MDF)of sulfur isotopes,implying that the ore-forming materials were potentially derived from the mantle lithosphere that was metasomatized and fertilized by subduction-related fluids released from slab during the Early Cretaceous.This study demonstrates the Bi-rich melts as significant gold scavengers in As-deficient ore-forming fluid,and highlights the fundamental role of the metasomatized and fertilized mantle lithosphere in the formation of giant lode gold deposits in the eastern North China Craton at ca.120 Ma.