Southwestern Guizhou Research Articles

Geological and geochemical characteristics of high arsenic coals from endemic arsenosis areas in southwestern Guizhou Province, China

Southwest Guizhou Province is one of the most important areas of disseminated, sediment-hosted-type Au deposits in China and is an important area of coal production. The chemistry of most of the coals in SW Guizhou is similar to those in other parts of China. Their As content is near the Chinese coal average, but some local, small coal mines contain high As coals. The highest As content is up to 3.5 wt.% in the coal. The use of high As coals has caused in excess of 3000 cases of As poisoning in several villages. The high As coals are in the Longtan formation, which is an alternating marine facies and terrestrial facies. The coals are distributed on both sides of faults that parallel the regional anticlinal axis. The As content of coal is higher closer to the fault plane. The As content of coal changes greatly in different coal beds and different locations of the same bed. Geological structures such as anticlines, faults and sedimentary strata control the distribution of high As coals. Small Au deposits as well as Sb, Hg, and Th mineralization, are found near the high As coals. Although some As-bearing minerals such as pyrite, arsenopyrite, realgar (?), As-bearing sulfate, As-bearing clays, and phosphate are found in the high As coals, their contents cannot account for the abundance of As in some coals. Analysis of the coal indicates that As mainly exists in the form of As5+ and As3+, perhaps, combined with organic compounds. The occurrence of such exceptionally high As contents in coal and the fact that the As is dominantly organically associated are unique observations.

Au-Sb association and fractionation in micro-disseminated gold deposits, southwestern Guizhou—geochemistry and thermodynamics

The dual geochemical character of paragenesis and fractionation between gold, arsenic and antimony in micro-disseminated gold deposits in southwestern Guizhou is discussed in terms of spatial distribution of independent deposits, lateral and vertical enrichment, mineralization stage and factor and correlation analyses. Thermodynamic calculations of solubility and speciation of gold and antimony minerals indicate that gold is transported in hydrothermal solution as Au(HS) - 2 and antimony is mainly as Sb (OH 0 3 ) although HSb 2 S - 4 may be of increasing importance in acid environment at low temperatures during the late stage of mineralization. Changes in physicochemical conditions hold the key to the association and fractionation between gold and antimony. Gold and antimony response differently to physicochemical variations because they are distinct from each other in soluble speciation and mineral solubility, leading to precipitation at different times and localities during hydrothermal evolution.

Crude oil as carrier of gold: petrological and geochemical evidence from Lannigou gold deposit in southwestern Guizhou, China

Organic matter is related closely to mineralization of Lannigou gold deposit in southwestern Guizhou, China. Regionally, the distribution of organic carbon agrees well with that of faults within which gold deposits are hosted. Studies on organic petrology show that pyrobitumen, which is related most closely to mineralization, adheres to quartz vein or fills quartz veinlet. Proton-induced X-ray emission (PIXE) analysis shows an evident abundance of Au in pyrobitumen. Pyrobitumen paragenetically associates with pyrite and arsenopyrite which are the main carrier minerals of Au. The thermal simulation experiment indicates that about 99% of Au will be concentrated in oil phase in the coexisting system of oil and brine and rock. The role of crude oil in ore-forming process is: as carrier of Au, crude oil moves upwards, and undergoes thermal decomposition and thermochemical reduction when it encounters the oxidizing fluid within the Trassic turbidity; Au is thus released from crude oil, reduced and precipitated.

Genesis of Carlin-type gold deposits in southwestern Guizhou Province, China

A solution containing nanometer-sized pure gold particles was prepared with the hydrolysisreduction method. As observed under the electron microscope, the gold particles were as large as 2–20 nm in size. Different kinds of mineral and rock were put into the solution and the experimental result showed that the nanometer-sized gold particles are obviously adsorbed on sulfide minerals, native copper and carbonaceous rocks. This experimental result is consistent with the actual geological observation. On this basis a better explanation is presented of the genesis of the Carlin-type gold deposits.

Two kinds of Carlin-type gold deposite in southwestern Guizhou, China

Based on the organic geochemical studies on two typical Carl in-type deposits in southwestern Guizhou, as well as the comparison between the two deposits in terms of geological background, igneous rock, paleo-oilfield, lithofacies and paleogeographical and geochemical features, two kinds of Carlin-type deposit were proposed: Lannigou Type and Getang Type. The former includes Lannigou, Banqi and Yata gold deposits. These deposits are hosted by turbidite, geographically situated in the southwest of the mineralized district, and related genetically to paleo-oilfields. The latter includes Getang, Zimudang and Dachang gold (mercury and thallium) deposits, situated geographically in the northwest of the mineralized district where Emeishan basalt commonly occurs. These deposits are associated with reduction of coaly organic matter.

A study on the relations between Ultrabasic Dikes and fine disseminated gold deposits in southwestern Guizhou Province as exemplified by Zimudang large-sized gold deposit

The relations between ultrabasic rocks and gold deposits in time, space and genesis are discussed in this paper. The research results show that the ore-forming materials of the gold deposits is characteristic of crust-mantle mixing. The formation of the gold deposits is related with the activity of juvenile fluids along with the intrusion of ultrabasic dikes. The ascending juvenile fluids not only offered part of the gold, water and mineralizers for gold mineralization, but also promoted the remobilization, deposition and enrichment of gold in crustal sediments.

On the Mechanism of Transformation from Primary Ores into Oxidized Ores in Finely Disseminated Gold Deposits

Abstract: This paper, taking the finely disseminated gold deposits in southwestern Guizhou and northwestern Guangxi as examples, discusses the difference between the occurrence of primary ores and that of oxidized ores, analyzes the occurrence mechanism in terms of crystallochemistry and geochemistry, and especially studies the chemical model for supergene leaching transformation of clay minerals in the two types of ores. This study proposes a new idea for dressing and smelting technology for primary gold ores.

The micro-disseminated gold deposits of exhalative genesis in southwestern Guizhou, China

The micro-disseminated gold deposits of exhalative genesis in southwestern Guizhou, China

Preliminary study on light hydrocarbons in ore-forming fluids of gold and antimony deposits in southwestern Guizhou, China

Preliminary study on light hydrocarbons in ore-forming fluids of gold and antimony deposits in southwestern Guizhou, China

Physicochemical conditions of differential mineralization of Au and As in gold deposits, southwest Guizhou Province, China

The conditions under which gold and arsenic are enriched separately during mineralization in gold deposits in southwestern Guizhou Province were described and the thermodynamic calculations gave: 200–150°C at 400 × 10−6 -300 × 106 Pa (corresponding to a depth between 1.6 km and 1.2 km); lgf o2,−40 to -35 Pa; lgf s2, -20 to−16 Pa; pH 5.0 -4.2 and Eh -0.53 V.

Geology and geochemistry of three sedimentary-rock-hosted disseminated gold deposits in Guizhou Province, People's Republic of China

Five sedimentary-rock-hosted disseminated gold deposits have been discovered since 1980 in southwestern Guizhou Province (PRC). Submicron-sized gold is disseminated in silty carbonate and carbonaceous shale host rocks of Permian and Triassic age. Arsenic, antimony, mercury, and thallium accompany the gold. Associated hydrothermal alteration resulted in decarbonatization of limestone, silicification, and argillization, and depletion of base metals, barium, and many other elements. Organic material occurs in most host rocks and ores. It was apparently devolatilized during a regional heating event that preceded hydrothermal activity, and thus was not mobilized during mineralization, and did not affect gold deposition. The geologic setting of the Guizhou deposits includes many features that are similar to those of sedimentary-rock-hosted deposits of the Great Basin, western United States. The heavy-element suite that accompanies gold is the same, but base metals are even scarcer in the Guizhou deposits than they are in U.S. deposits. The Guizhou deposits discovered to date are smaller than most U.S. deposits and have no known spatially associated igneous rocks.