Mineralogical characteristics of polymetallic sulfides from the Deyin-1 hydrothermal field near 15°S, southern Mid-Atlantic Ridge

A seafloor hydrothermal field, named Deyin-1 later, near 15°S southern Mid-Atlantic Ridge（SMAR） was newly found during the 22 nd cruise carried out by the China Ocean Mineral Resources Research ＆ Development Association（COMRA）. Sulfide samples were collected at three stations from the hydrothermal field during the26 th cruise in 2012. In this paper, mineralogical characteristics of the sulfides were analyzed with optical microscope, X-ray diffractometer, scanning electron microscope and electron microprobe to study the crystallization sequence of minerals and the process of hydrothermal mineralization. According to the difference of the ore-forming metal elements, the sulfide samples can be divided into three types：（1） the Ferich sulfide, which contains mainly pyrite and chalcopyrite;（2） the Fe-Cu-rich sulfide consisting predominantly of pyrite, chalcopyrite and isocubanite, with lesser amount of sphalerite, marmatite and pyrrhotine; and（3） the Fe-Zn-rich sulfide dominated by pyrite, sphalerite and marmatite, with variable amounts of chalcopyrite, isocubanite, pyrrhotine, marcasite, galena and gratonite. Mineral precipitations in these sulfides are in the sequence of chalcopyrite（isocubanite and possible coarse pyrite）, fine pyrite,sphalerite（marmatite）, galena, gratonite and then the minerals out of the dissolution. Two morphologically distinct generations（Py-I and Py-II） of pyrite are identified in each of the samples; inclusions of marmatite tend to exist in the coarse pyrite crystals（Py-I）. Sphalerite in the Fe-Zn-rich sulfide is characterized by a＂chalcopyrite disease＂ phenomenon. Mineral paragenetic relationships and a wide range of chemical compositions suggest that the environment of hydrothermal mineralization was largely changing. By comparison, the Fe-rich sulfide was formed in a relatively stable environment with a high temperature, but the conditions for the formation of the Fe-Cu-rich sulfide were variable. The Fe-Zn-rich sulfide was precipitated during the hydrothermal venting at relatively low temperature.

Petrophysical characteristics of rocks and sulfides from the SWIR hydrothermal field

Study of petrophysical properties of rocks in seafioor hydrothermal fields has great significance for inves- tigation of seafloor hydrothermal activities, especially for polymetallic sulfides prospecting. In the present study, based on the current experimental conditions, we conducted systematic experiments to measure the magnetic susceptibility, electrical resistivity, porosity, density, as well as acoustic wave velocity of seafloor rocks and sulfides. Subsequently, we measured the physical characteristics of hydrothermal sulfides, basalts and peridotites which were collected from newly discovered seafloor hydrothermal fields at 49.6°E, 50.5°E, 5 1°E, 63.5°E, and 63.9°E of the Southwest Indian Ridge （SWIR）. Previously available and newly collected data were combined to characterize the physical differences between polymetallic sulfides and rocks. We also discussed the impact of hydrothermal alteration on the bedrock and demonstrated how these petrophysical properties of rocks can help in geophysical prospecting of seafloor hydrothermal fields as indicators.

Quantitative prediction process and evaluation method for seafloor polymetallic sulfide resources

Seafloor polymetallic sulfide resources exhibit significant development potential. In 2011, China received the exploration rights for 10,000 km2 of a polymetallic sulfides area in the Southwest Indian Ocean; China will be permitted to retain only 25% of the area in 2021. However, an exploration of seafioor hydrothermal sulfide deposits in China remains in the initial stage. According to the quantitative prediction theory and the exploration status of seafloor sulfides, this paper systematically proposes a quantitative prediction evaluation process of oceanic polymetallic sulfide resources and divides it into three stages： prediction in a large area, prediction in the prospecting region, and the verification and evaluation of targets. The first two stages of the prediction process have been employed in seafloor sulfides prospecting of the Chinese contract area. The results of stage one suggest that the Chinese contract area is located in the high posterior probability area, which indicates good prospecting potential area in the Indian Ocean. In stage two, the Chinese contract area of 48^-52~E has the highest posterior probability value, which can be selected as the reserved region for additional exploration. In stage three, the method of numerical simulation is employed to reproduce the ore-forming process of sulfides to verify the accuracy of the reserved targets obtained from the three-stage prediction. By narrowing the exploration area and gradually improving the exploration accuracy, the prediction will provide a basis for the exploration and exploitation of seafloor polymetallic sulfide resources.

Mineralogical Characterization of a Polymetallic Sulfide Ore to Improve Silver Recovery

Based on the mineralogical characterization for the polymetallic sulfide ore, the way to improve silver recovery was studied. The results showed that silver was the most valuable metal whose grade was 448.82 g/t Ag, while 0.118% Cu, 1.65% Pb and 1.06% Zn may be comprehensively utilizated. The main silver-bearing minerals were argent and aregentite which accounted for 87.18% of total silver. Argentite and other metal minerals were distributed in the gangue minerals in complex forms. Argentite grains of 33.76% minus 50 μm indicated that a fine grinding scheme was necessary to enhance the degree of dissociation, and meanwhile selective grinding must be considered to prevent a complete grinding of coarse grains. The optimum regrinding fineness in the Cu flotation was determined as 73% minus 37 μm, while grains of 68.5% minus 74 μm in one-stage grinding remained unchanged as much as possible. Consequently, silver recovery increased to 2.68%, as well as the content of Pb simultaneously decreased from 7.26% to 2.68% in the Cu concentrate. From the lead pyrometallurgical point of view, recovering larger amounts of silver and lead at the expense of decreasing the grade of lead to a suitable level is not only economically viable for the plant, but also convenient for subsequent processing. Silver and lead recovery increased to 13.18% and 12.58%, respectively, while the Pb grade decreased from 53.1% to 46.12% for the Pb concentrate.

Ore-controlling Characteristics of Synchronous Faults of Dongshengmiao Polymetallic Sulfide Deposits in Inner Mongolia

1 Introduction The Dongshengmiao deposit is a super-large Zn-Pb polymetallic sulfide deposit which occurring in the Langshan-Zhaertaaishan metallogenic belt,and located in the western margin of the North China Platform.The ore-bodies of Dongshengmiao deposits are mainly hosted in the second Formation of Langshan Group.There are some studies on the geological characteristics(Peng et al.,2004),geological and

The deep structure of the Duanqiao hydrothermal field at the Southwest Indian Ridge

Polymetalic sulfide is the main product of sea-floor hydrothermal venting, and has become an important sea-floor mineral resources for its rich in many kinds of precious metal elements. Since 2007, a number of investigations have been carried out by the China Ocean Mineral Resources Research and Development Association（COMRA）cruises（CCCs） along the Southwest Indian Ridge（SWIR）. In 2011, the COMRA signed an exploration contract of sea-floor polymetallic sulfides of 10 000 km2 on the SWIR with the International Seabed Authority. Based on the multibeam data and shipborne gravity data obtained in 2010 by the R/V Dayang Yihao during the leg 6 of CCCs21, together with the global satellite surveys, the characteristics of gravity anomalies are analyzed in the Duanqiao hydrothermal field（37°39′S, 50°24′E）. The ＂subarea calibration＂ terrain-correcting method is employed to calculate the Bouguer gravity anomaly, and the ocean bottom seismometer（OBS） profile is used to constrain the two-dimensional gravity anomaly simulation. The absent Moho in a previous seismic model is also calculated.The results show that the crustal thickness varies between 3 and 10 km along the profile, and the maximum crustal thickness reaches up to 10 km in the Duanqiao hydrothermal field with an average of 7.5 km. It is by far the most thicker crust discovered along the SWIR. The calculated crust thickness at the Longqi hydrothermal field is approximately 3 km, 1 km less than that indicated by seismic models, possibly due to the outcome of an oceanic core complex（OCC）.