Pretreatment and thiosulfate leaching of refractory gold-bearing arsenosulfide concentrates

A hydrometallurgical process for refractory gold-bearing arsenosulfide concentrates at ambient temperature and pressure was presented, including fine grinding with intensified alkali-leaching （FGIAL）, enhanced agitation alkali-leaching （EAAL）, thiosulfate leaching and displacement. Experimental results on a refractory gold concentrate showed that the total consumption of NaOH in alkaline leaching is only 41% of those theoretically calculated under the conditions of full oxidization for the same amount of arse- nides and sulfides transformed into arsenates and sulfates, and 72.3% of gold is synchro-dissoluted by thiosulfate self-generated during alkaline leaching. After alkaline leaching, thiosulfate leaching was carried out for 24 h. The dissolution of gold is increased to 91.9% from 4.6% by cyanide without the pretreatment. The displacement of gold by zinc powder in the solution gets to 99.2%. Due to an amount of thiosulfate self-generated during alkaline leaching, the reagent addition in thiosulfate leaching afterwards is lower than the normal.

Ultrafine milling for the processing of gold-bearing sulphides

Ultrafine Milling technology is used to treat gold-bearingsulphides and to investigate the effects of minerals size, millingtime, liquid/solid ratio, NaCN consumption and leaching aid onleaching rate of gold. The results indicate that shorter treatingtime, decrease of NaCN consumption of 60/100 and increase of goldleaching rate of 15/100 can be ob- tained by the ultrafine millingtechnology compared with traditional cyanide leaching. Potentialexists for the new pro- cess to form the basis for an economicallyprocess for treatment of gold-bearing sulphides.

Amur Gold-Bearing Belt: Geotectonic Position and Perspectives for Revealing New Deposits of Precious Metals

The ore-bearing belts, specialized for precious metals, are substantia ted to exist in the south Far East of Russia. The longest of which is the Amursk y gold-bearing belt extended from the Amur River mouth to the Ussuri River lowe r course and further to the southwest on China territory, probably, to the Sungar i River head. The fact that we have distinguished the Amursky and other gold-be a ring belts, make it possible to reevaluate the perspectives of the South Far Eas t of Russia and North-East China for new deposits of precious metals.

THIOUREA LEACHING OF GOLD FROM A CALCINE OF GOLD-BEARING ARSENICAL PYRITE CONCENTRATE

The thiourea leaching of gold from the calcine of gold-bearing arsenical pyrite concentrate of Kangjiawan mine was studied.The effects of the leaching time,the concentrations of thiourea,hydrochloric acid and initial ferric ion on the leaching recovery of gold were investigated,and a regressive model has been established,which showed that the concentrations of thiourea and hydrochloric acid were the most important factors,leaching time the second,and concentration of the initial ferric ion the least・Under the optimal conditions,that is,temperature 50℃,the ratio of liquid to solid 4:1,thiourea 12g/L,hydrochloric acid 1 mol/L,and initial ferric ion 1 g/L,the leaching recoveries of gold and silver were more than 81%and 73%,respectively.The increase of silver recovery and the reduction of thiourea consumption could be attained when sodium sulphite was added.

Gold-bearing formations and their evolution in central Inner Mongolia

In central Inner Mongolia, five gold bearing formations (Xiajining, Dongwufenzi, Wulashan, Baiyunebo and Bainaimiao Groups) belong either to volcano sedimentation or clasolite sedimentation. They formed in different tectonic environments such as an Archean rift zone (Xiajining and Dongwufenzi Groups), an Early Proterozoic stable basin (Wulashan Group), a Middle to Late Proterozoic continental rift zone (Baiyunebo Group), and a Paleozoic island arc environment (Bainaimiao Group). Gold contents in the gold bearing formations in the area are higher than those of other gold bearing formations in the North China Craton. However, as most gold bearing formations in the area are limited, there are a few big gold deposits in central Inner Mongolia. Gold contents in all formations were strongly influenced by migmatization and ductile shearing, the former process prompting mobilization, and the latter process resulting in gold enrichment in ductile shear zones. During the development of Archean to Proterozoic gold bearing formations, gold migrated from the mantle to the crust, then through the crust, finally deposited at the earth’s surface.

ON GOLD-BEARING CHARACTERISTICS OF GEOSYNCLINAL TECTONIC LAYER IN XUEFENG MOUNTAIN TECTONIC BELT,HUNAN,CHINA

1. Material composition of the geosynclinal tectonic LayerThe geosynclinal tectonic layer is mainly composed of the following two parts: sandyslate rocks of Precambrin and volcanic rocks inbeded within the sand-slate rocks.The sandy-slate rocks embrace the chemical compositional characteristics of light metamorphic rocks: SiO2=54.5681.63（Wt%）, with average of 63.96（wt%）（n=58, the same as following）; Al2O3=9.4717.75（wt%）, with average of 15.36（wt%）, and Al2O3】K2O+Na2O+CaO; the content of （FeO+Fe2O3） varies greatly with FeO】Fe2O3; （CaO+MgO）=0.789.22 （wt%）with average of 23 （wt%）, and MgO】CaO; the ratios of K2O/Na2O rang from 2 to 4（】1）. By comparing all this chemical data with that of the other kind rocks, We can know that the sand y-slate rocks were the eunic and /or bathyal sediments which formed under the strongly active eugeosynclinal tectonic setting.

Dual origins of Xiaoqinling gold-bearing quartz veins:Fluid inclusion evidence

Fluid inclusion research in Archean metamorphic rocks, Yanshanian granite and gold-bearing quartz veins shows that regional metamorphic fluids are high temperature and high saline, Yanshanian post-granitic fluids are CO2-bearing low saline, and ore-forming fluids are also CO2-rich low saline. In gold-barren/free parts of quartz veins in gold deposits, daughter mineral-bearing high saline inclusions related with metamorphic fluids remained. This proclaims quartz veins hosting gold ores might have been formed in early metamorphism, and overlapped or mineralized by late Yanshanian gold-bearing fluids.

Kerogen——as a sort of organic bearer of gold in gold-bearing formations

Organic component, organic carbon and gold content analyses were used to study the relationship between gold mineralization and organic matter in major host rocks of three different chronological gold-bearing formations of South China. The results show that the organic matter of host rocks in various chronological major gold-bearing formations of South China has associated with gold mineralization in genesis. There is a positive correlation between gold and organic carbon in the host rocks of gold-bearing formations. Gold element was mainly enriched in insoluble organic matter——kerogen. Gold content of the kerogen is commonly higher from a few tens to several hundred times than that of the whole rocks, up to 5%—40% gold of the whole rocks. Gold remaining in the kerogen was considered an organic group of the kerogen to combine with ionic gold in solution through surface absorption, ion exchange complex reaction and chelation so that the kerogen could have become an important sort of organic bearer

Timing of mineralization at the Shihu gold deposit in the middle segment of the Taihang Mountain, China

The Shihu gold deposit, located in the middlesouth section of the core of the Fuping mantle branch structure, is hosted in the Archean Fuping Group and adjacent to the quartz diorite porphyrite. The gold deposit is the only large gold deposit with reserves of more than 30 tons gold discovered in western Hebei Province so far. In order to constrain the timing of mineralization of this ore deposit, this paper focuses on the isotopic dating of zircon and pyrite. Zircons in gold-bearing quartz veins are magmatic in origin and no hydrothermal zircon has been found in such quartz veins, indicating that zircons were derived from the wall rocks. U–Pb ages of zircons fall mainly in the two domains: 2492 ± 82 and 136 ± 4 Ma, respectively,indicative of the contribution of the Fuping-Group TTG gneiss and Yanshanian igneous rocks, respectively. The Re–Os isotopic compositions of pyrites in the gold-bearing quartz veins yield an isochron age of 127 ± 31 Ma. Combined with other dating results, we suggest that the main metallogenic age of the Shihu gold deposit is 120–127 Ma.

Structural Control of Auriferous Mineralization in the Birimian: Case of the Agbahou Deposit in the Region of Divo, Côte d’Ivoire

Located in the southwestern of the Oume-Fettekro greenstone belt, the Agbahou gold deposit is controlled by structural factors. Geophysics, teledetection and core data suggest the presence of NE and NW faults. However, the NE-faults define two major shear zones (ATZ: Agbahou Tectonic Zone and WTZ: West Tectonic Zone) that control the Agbahou gold mineralization. These first order structures are subparallel to the regional tectonic grain mostly north-east oriented. They seem to respectively develop on the both arms (eastern and western) of an anticline moderately plunging ~25° towards northeast. Each shear-zone contains several second-order shear-zones or lenses of variable direction and of 50° - 80° dip. NW-faults however correspond to strike-slip faults and their development should be related to transcurrent tectonics. They acted as control channels on the distribution of gold mineralizations. The ductile-brittle character of shear-zones favored the ascent of hydrothermal fluids and the formation of multiple auriferous quartz veins: veins Type IIa and veins Type IIb relating respectively to the shear-veins and extensional veins. However, Agbahou also shows the existence of a disseminated sulphides-bearing mineralization within host-rocks. At Agbahou, the precipitation of gold probably occurred in a post to late ductile-brittle deformation period.

Experimental Study on Gold Dissolution from Hosting Minerals of the Hadamengou Gold Deposit and the Implications

The Hadamengou gold deposit is located in western part of the northern margin of the North China craton. It is a hydrothermal deposit related to alkaline magmatism. Dissolution of Au, Fe from pyrite and iron oxide （including magnetite and hematite） individual minerals in the three main types of ore shows： in iron oxides （magnetite and hematite）, Au and Fe were dissolved simultaneously and their solubilities are positively correlated, which means Au is mainly chemical-bonded （lattice gold） and/or colloidal-adsorbed in iron oxides; while in pyrite, on the contrary, Au dissolution obviously lags behind Fe and the solubility of Au shows negative relationship with that of Fe, which indicates Au is mainly hosted as grains of elemental gold （or native gold） within pyrite. Previous studies revealed that the Hadamengou gold deposit is characterized by intensive K-feldspathization and holds high content of iron oxides occasionally replaced by sulfides, which was caused by oxidizing K-enriched alkaline fluids under a stretching geodynamic setting. These geological features, together with the high Au-content in iron oxides, comparable with that of the Olympic Dam deposit in South Australia, suggest that this deposit is the first example of iron oxide-type gold deposits in China.

Sm-Nd ISOTOPIC AGE OF LAMPRO PHYRES IN THE GEZHEN GOLD BEARING SHEAR ZONE ON HAINAN ISLAND AND ITS GEOLOGICAL IMPLICATIONS

Sm Nd isotopic compositions of eight lamprophyre samples, which come from the Gezhen gold bearing shear zone on western Hainan Island, are measured. The Sm Nd isochron age is 495.98±13.14 Ma, (143Nd/144Nd)0=0.512094, εNd(t) ranges from +1.80 to +2.00 and TDM from 982 Ma to 1196 Ma (average: 1060 Ma). The authors point out that the whole rock Sm Nd isochron age (495.98±13.14 Ma) really represents the petrogenetic age of lamprophyre and the time of magmatism during subsequent subduction.

Fluid Inclusion Evidences for the P-T Conditions of Quartz Veins Formation in the Black Shale-Hosted Gold Deposits, Bodaybo Ore Region, Russia

The P-T conditions of auriferous and barren quartz veins from Kopylovsky,Kavkaz and Krasnoye gold deposits in Proterozoic black shales of Bodaybo ore region are presented the first time in this study.Fluid inclusions trapped in auriferous quartz are aqueous Na±K-Mg chloride with salinity of 6 wt.%-8.8 wt.%NaCleqv.Homogenization temperatures vary from 260 to 350℃,and calculated trapping pressures are 1.2-1.6 kbar.The fluids trapped in barren quartz have more complicated compositions with Na,K,Mg and Fe chlorides,salinity up to 13 wt.%NaCleqv,and homogenization temperatures ranging between 140 and 280℃.The volatiles in fluids are dominated by H2O,followed by CO2 with minor amounts of CH4 and N2.We suppose that auriferous and barren quartz veins have been formed due to the basic metamorphogenic fluid as evidenced by the close slat and gas fluid composition.