REE and Trace Element Geochemistry of Yinachang Fe-Cu-REE Deposit, Yunnan Province, China

REE and other trace elements in ores, wall rocks, alkaline volcanic rocks and diabase dikes have been determined in the Yinachang Fe-Cu-REE deposit. Comparative studies of REE and trace element geochemical characteristics of these geological bodies indicate that the ores and alkaline volcanic rocks contain abundant REE and Y ({65.9}-{4633})×10+{-6}, with higher abundances of As, Mo, Nb, Co and U than those of the crust. Their chondrite-normalized patterns show a strong enrichment of LREE and a positive Eu anomaly, in contrast to those of the dolomites which are characterized by slight LREE enrichment and moderate negative Eu anomaly. The REE patterns of ores are similar to those of hydrothermal sediment cores in the East Pacific Rise, whereas the REE patterns of dolomites are similar to those of PAAS (Post-Archean Average Shale). In combination with the geological setting of the deposit, the primary ore-forming fluids might have higher REE and volatile elements, and might have been derived from mantle degassing, or the alkaline volcanic magmas. The Yinachang Fe-Cu-REE ore deposit is considered to be of volcanic exhalation-hydrothermal sedimentary origin.

Complexity and Geodynamics of Ore-accumulating Basins in the Qinling Orogenic Belt,China

Researches were made of different continental-margin and intraplate basin systems in the Qinling microplate in terms of hydrothermal deposition, geodynamics of basin formation, hydrothermal sedimentary rock facies, syntectonics in the basins, and the styles of ore accumulation in the basins.

Mineralization Zoning in Yindongzi-Daxigou Barite-Siderite, Silver-Polymetallic Deposits in the Qinling Orogen, China

The Yindongzi\|Daxigou strata\|bound barite\|siderite, silver\|polymetallic deposits discovered in the Qinling orogen are hosted within flysch facies in a deep\|water fault\|controlled basin on the passive northern margin of the Qinling microplate. The orebodies occur in a series of hydrothermal depositional rocks. Mineralization zoning is characterized by Fe\|Ba←Ba\|Cu←Pb\|Ag→Cu\|Ag→Pb→Au. This is obviously a gradational transition mineralization from vent\|proximal mineralization to more distal mineralization. In this gradational transition between Chefanggou and Yindongzi, vent\|proximal mineralization consists of silver\|polymetallic orebodies (Pb\|Ag), which is the center of hydrothermal mineralization. The Chefanggou Ba\|Cu ore district in the west and the Yindongzi Cu\|Ag ore district in the east represent vent lateral mineralization. Distal mineralization in the west is represented by the Daxigou Fe\|Ba ore district while distal mineralization in the east is represented by the Pb ore district. Thick massive, laminated barren albite chert and jasperite, sometimes with minor silver\|ploymetallic mineralization of commercial importance, and pyritization in rocks feature more distal mineralization. Geochemical anomalies of Au\|As associations are found in ankerite phyllite and muddy sandstone. Actually, Au deposits are dominantly controlled by the late brittle\|ductile shear zone.

Diagenetic-metallogenic ages of pyritic cherts and their implications in Mojiang nickel-gold deposit in Yunnan Province,China

Diagenetic-metallogenic ages of pyritic cherts formed by the syn-sedimentation of hydrothermal vent and ages of the Jinchang Rock Formation in the Mojiang large nickel-gold deposit in the Ailaoshan gold metallogenic belt have been discussed on the basis of chronology of isotopic geochemistry. Nickel-gold-bearing pyritic cherts in the mining were formed by syn-sedimentation of hydrothermal vent in the Late Devonian, i.e. age by Sm-Nd isochronal method (t) = (358±8.6) (2σ) Ma and age by Rb-Sr isochronal method (t) = (354.7±0.72) (2σ) Ma. On the other hand, deep-water cherts from the Jinchang Rock Formation of the Upper Devonian in the area were initiated at the same time; that is, age by Sm-Nd isochronal method (t) = (359(+21) (2(7) Ma and age by Rb-Sr isochronal method (t) = (358.02±0.30) (2σ) Ma.

Sm-Nd isotopic geochronologyof the Yinachang Fe-Cu-REE deposit at Wuding,Yunnan Province and its genetic significance

Sm-Nd isotope systematics of ores and fluorites places precise time constraints on REE mineralization of the Yinachang Fe-Cu-REE deposit in Yunnan Province which occur in the Proterozoic Kunyan group. The ore-related fluorites contain high abundant REE, and show a strong enrichment of LREE and a positive Eu anomaly, which is in marked contrast to post-ore fluorites that are HREE en-riched. The Sm-Nd isochron ages of the ores and fluorites are 1539±40 Ma and 1617±100 Ma, respectively, and calculated εNd(t) are ?4.6 and ?3.2. Accurate age determinations of the mineralization demonstrate that the REE mineralization took place during early Mesoproterozoic. Together with other geological evidence from the ore deposit, the primary REE-bearing ore-forming fluids are suggested to have been derived from the Enriched Mantle, and the Yinachang Fe-Cu-REE ore deposit is of volcanic exhalation- hydro-thermal sedimentary origin. This study also imply that the sudden large-scale REE mineralization in the Mesoprotero-zoic epoch may have been induced by alkaline-rich anoro-genic magmatism which occurred at marginal rifts of the continent in the Mesoproterozoic.