Quartz Vein-type Gold Deposit Research Articles

Chenguodaite (Ag9FeTe2S4): a new tellurosulfide mineral from the gold district of East Shandong Peninsula, China

Chenguodaite, approved by IMA-CNMMN (2004-042a), was discovered in the Bunan quartz vein-type gold deposit in the gold district of East Shandong Peninsula. The mineral occurs in high grade Au-Ag-Cu ores, coexisting with galena, chalcopyrite, hessite, electrum, unnamed Ag6TeS2 and Ag16FeBiTe3S8, enclosed and replaced by native silver and acanthite. In the reflected light microscope, the mineral has light gray color, indistinguishable anistropism and hardness around 2–3. The color indices of chenguodaite relative to ICE C illuminator are: x=0.3027, y=0.3076, Y=25.78%,-λd=474 nm, Pe=3.68%, similar to those of canfieldite. The average chemical composition from 16 microprobe analyses is Ag8.97Fe1.00Te1.99S4.04, idealized to Ag9FeTe2S4. The polycrystalline X-ray diffraction of chenguodaite by Gandolfi camera and synchrotron oscillation photography results in 67 reflections with the 12 strongest being (relative intensity in bracket): 6.742(69), 6.416(39), 5.951(33), 3.265(100), 2.981(24), 2.649(22), 2.25(24), 2.188(71), 2.142(22), 2.123(31), 2.044(23), 1.949(33), which are indexed to a primitive orthorhombic cell with a=12.769 (2) A, b= 14.814(2) A, c= 16.233 (1) A, V= 3070.6 A3, Z = 9, Dcal.=6.85 g/cm3. The name is for the late Prof. Chen Guoda, a famous Chinese geologist and the founder of Diwa-Geodepression theory of tectonics.

Mechanism of inversion metallogeny of quartz vein type gold deposits in the Xiaoqinling region

There are a lot of important gold-bearing quartz veins in the Xiaoqinling metamorphic core complex. The quartz veins are strictly controlled by shear zones. Stress analysis indicates that the metallizing process of the Xiaoqinling gold deposits of quartz vein type can be divided into two stages. At the first stage, the shear zones were formed in an extensional environment, and the temperature was higher and thr buried depth was greater; at the second stage, the brittle thrusts were superimposed in ductile shear zones after the tectonic stress field turnrd form the extension to compression. The ore-bearing fluids were concentrated in these weak positions, and the gold deposits of quartz vein type were developed.

Granitoid-hosted gold deposits in the Anjiayingzi District of Inner Mongolia, People's Republic of China

The Anjiayingzi district contains several mesothermal, quartz vein-type gold deposits which are hosted by a Mesozoic quartz monzonite (Jiguanzi pluton). A second pluton (Kalaqin granite), which is older than the quartz monzonite, is not mineralized. The granitic plutons are situated in a basement sequence of early Precambrian gneisses. Rhyolite dikes occupy the same fracture systems as the mineralized quartz veins and the dikes crosscut the veins; thus the age of mineralization is constrained between that of the host pluton (124-132 Ma, K-Ar and Rb-Sr biotite ages) and the dikes (122 + or - 1 Ma, Rb-Sr whole-rock isochron).Gold deposits consist of quartz sulfide veins and alteration zones in faults and fractures within the Jiguanzi quartz monzonite. Hydrothermal alteration formed quartz-sericite-pyrite assemblages as vein selvages and propylitic assemblages which extend up to several decimeters outward from the selvages. Mineralizing fluids removed Na, Ca, Sr, and Ba from wall rock, and added Mn, K, Rb, S, CO 2 and the ore elements Au, Cu, Pb, and Zn. Fluid inclusions in vein and selvage quartz contain low-salinity fluids with about 10 to 50 mole percent CO 2 . Total homogenization temperatures of 300 degrees + or - 30 degrees C (2Sigma ) are consistent with temperature estimates from chlorite geothermometry. Inclusion evidence of CO 2 - H 2 O unmixing fixes the trapping pressure at 0.5 to 1.1 kbars. Fluid unmixing may have been a factor in causing gold precipitation.Most whole-rock delta 18 O values of the Jiguanzi host pluton range from 7.6 to 8.2 per mil (SMOW) and these probably represent magmatic compositions. Lower values (0-5ppm) were obtained from two samples of the pluton and from the rhyolite dikes. These low delta 18 O values reflect postmagmatic alteration. Limited S-O-H isotope data from pyrite and vein quartz indicate that the hydrothermal fluids were of meteoric origin and that S was leached from the basement gneisses. Neither the Jiguanzi quartz monzonite, which hosts the gold ore, nor the rhyolite dikes, with which gold mineralization is most closely associated in the field, are anomalously enriched in gold. Therefore we rule out the granitic intrusions as a source of ore elements or fluid.

Genesis and geological-geochemical characters of the Rushan gold deposit, Shandong, China

The Rushan gold deposit, explored in recent years in the Jiaodong area, Shandong Province, is a quartz vein-type gold deposit hosted in granite. The temperature of its major mineralization episode is between 220°C and 280°C. The salinity of the ore-forming fluid is 5 % to 9% NaCl equivalent, with H2O and CO2 as the dominant gas constituents. The fluid is rich in Na+, Ca2+ and Cl−, but relatively impoverished in K+ and F−, characterized by either Ca2+ > Na+ > K+ (in three samples) or Na+ > Ca2+ > K+ (in six samples). Hydrogen and oxygen isotopes in the ore-forming fluid are highly variable with δ18 $$O_{H_2 0} $$ ranging between − 7.70‰ and 5. 97‰ and $$\delta D_{H_2 0} $$ between − 128‰ and − 71‰. The possibility of lamprophyre serving as the source of gold can be excluded in view of its low gold content on the order of 2.5 × 10−9. Rb-Sr isochron ages of the deposit and the host Kunyushan granite are ( 104.8 ± 1.5) Ma and 134.6 Ma respectively with the respective initial Sr ratios of 0. 71307 and 0.7096. It is considered that the emplacement of the lamprophyre under a tensile environment had provided sufficient heat energy to facilitate deep circulation of meteoric water by which ore metals were extracted from the Kunyushan granite through long-term water-rock reaction.

Ore-forming information of quartz vein-type gold deposits——Taking Bainaimiao gold deposit

As an example, the ore-forming information of the Bainaimiao quartz vein-type gold deposits is dealt with. The second stage of gold mineralization (stage II) is an important ore-forming process; the intersected parts of main structure with other structures provide the favorable mineralization information; when the same form of pyrite crystals in one sample has two groups of thermoelectronic voltage, i. e. one group being positive and another group being negative and when the strong and relatively strong anomalies of Hg, F and/or As, Sb are overlapped by the weak anomalies of Au and Ag, the probable existence of blind orebodies at the depth could be predicted.

Fluid inclusions in quartz-pebbles of the gold-bearing Tarkwaian conglomerates of Ghana as guides to their provenance area

Quartz-pebbles of the early Proterozoic Au-bearing Tarkwaian conglomerates in Ghana reveal several original (inherited) pre-sedimentary fluid inclusions. These inclusions are CO2-N2 rich and display a distinct high density (up to 1.15 g/cm3). The unusual high density and composition compare well with CO2-N2-rich inclusions in quartz-vein type gold deposits of the Birimian Supergroup in Ghana and Burkina Faso. This type of fluid inclusions has not been reported from any other lode-gold deposit of greenstone affiliation and is thus a specific characteristic for Birimian-hosted gold deposits. Therefore, it can be used as an unequivocal pathfinder for epigenetic as well as for syn-sedimentary gold mineralization of the early Proterozoic of West Africa. The inherited fluid inclusions with the unique physicochemical characteristics suggest that the Tarkwaian quartz-pebbles and possibly some gold were derived from Au-quartz vein deposits comparable in mineralogy, petrography and genesis to those along the NW-margin of the Ashanti belt (e.g. Ashanti Mine, Prestea Mine).