Lai Jianqing

Ferrisepiolite: a new mineral from Saishitang copper skarn deposit in Xinghai County, Qinghai Province, China

Ferrisepiolite was discovered in the Saishitang copper skarn deposit in Xinghai County, Qinghai Province, China, as late- stage veinlets in copper-sulphide ores hosted in layered hedenbergite-andradite-actinolite skarn related to Indo-Sinian quartz diorite and Lower Permian metamorphosed clastic and carbonate rocks. Ferrisepiolite was formed in a highly oxidizing environment from low-temperature Fe-rich fluids and crystallized in cavities and fractures within the skarn-ore deposit. The mineral occurs in brown earthy and fibrous aggregates and shows brown to red-brown colour with strong pleochroism and 2nd order interference colours in a petrographic microscope. The measured refraction indices in white light for fibrous ferrisepiolite are: g 0 ¼ 1.628(8), a 0 ¼ 1.592-1.620. The thermal analysis of ferrisepiolite reveals a lower dehydration temperature of structural hydroxyl than sepiolite and a small weight loss (0.1-0.9%) in the range 500-700 � C. The average chemical composition from wet chemistry, X-ray fluorescence spectrometry (XRF) and electron probe microanalysis (EPMA) is (Fe 3þ

Ore‐forming Fluid Characteristics of the Saishitang Cu‐polymetallic Deposit in Qinghai Province, China

Saishitang Cu-polymetallic deposit is located in the southeast section of Late Paleozoic arcfold in the southeastern margin of Qaidam platform. Accoring to the geological process of the deposit, four mineralization episodes were identified: melt/fluid coexisting period (O), skarn period (A), first sulfide period (B) and second sulfide period (C), and 10 stages were finally subdivided. Three types of inclusions were classified in seven stages, namely crystal bearing inclusions (type I), aqueous inclusions (type II) and pure liquid inclusions (type III). Type I and II inclusions were observed in stage Ol, having homogenization temperature from 252 to 431°C, and salinities ranging from 24.3% to 48.0%. Type I inclusion was present in stage A1, having homogenization temperature from 506 to 548° C., and salinities ranging from 39.4% to 44.6%. In stage B1, type II and III inclusions were observed, with homogenization temperature concentrating between 300–400°C, and salinities from 0.4% to 4.3%. Type II inclusions were present in stage B2, with homogenization temperature varying from 403 to 550° C. In stage C1, type I and II inclusion commonly coexisted, and constituted a boiling inclusion group, having homogenization temperatures at 187–463°C, and salinities in a range of 29.4%–46.8% and 2.2%-11.0%. Type II and III inclusions were developed in stage C2, having homogenization temperature at 124–350°C, and salinities ranging between 1.6% and 15.4%. In stage C3, type II and III inclusions were presented, with a homogenization temperature range of 164–360°C, and salinities varying from 4.0% to 11.0%. The results of micro-thermal analysis show that fluids are characterized by high temperature and high salinity in stage O1 and A1, and experienced slight decrease in temperature and dramatic decrease in salinity in stage B1 and B2. In stage C1, the salinity of fluid increased greatly and a further decrease of temperature and salinity occurred in stage C2 and C3. Fluids boiled in stage C1. With calculated pressure of 22 MPa from the trapping temperature of 284–289°C, a mineralization depth of 2.2 km was inferred. Results of Laser Raman Spectroscopy show high density of H2O, CH4 and CO2 were found as gas composition. H-O isotope study indicates the ore-forming fluids were the mixture of magmatic water and meteoric water. Physicochemical parameters of fluids show oxygen and sulfur fugacity experienced a decrease, and redox state is weakly reducing. Along with fluid evolution, oxidation has increased slightly. Comprehensive analysis shows that melt exsolution occurred during the formation of quartz diorite and that metal elements existed and migrated in the form of chlorine complex. Immiscible fluid separation and boiling widely occurred after addition of new fluids, bringing about dissociation of chlorine-complex, resulting in a great deal of copper precipitation. In conclusion, Saishitang deposit, controlled by regional tectonics, is formed by metasomatism between highly fractionated mineralization rock body and wall rock, and belongs to banded skarn Cu-polymetallic deposit.

Rock-forming mechanism of Fenghuangshan rockbody in Tongling area

Based on the detailed geological investigation and record of galleries and drill holes, a new idea has been advanced that granodiorite is earlier than quartz monzodiorite porphyry. Both of them are products of two different magmatic intrusive activities. The analysis results of trace elements show that the Sr content is beyond any other crustal rock and the Th content is beyond that of Ta. The whole-rock analysis indicates that rockbody is rich in CaO and poor in K2O. In the composition of Pb istope of rockbody, the ratio of 207Pb to 204Pb is less than 15.60. All these show that the magma mainly comes from the upper mantle. Ti,Zr,Cr,Nb trace elements and the relation between the Gardini index(τ) and the Rittmann index(σ) indicate that the rockbodies are formed in the orogenic belt and island arc tectonic setting. The summation (ΣREE) and the characteristic value (m(La)/m(Yb)) of the rare earth elements show that the original rock is alkalic basalt. The analysis of the characteristic values of REE and the quantitative modeling calculation indicate that the rock-forming process is dominated by mixed crystallization. According to the analysis on the rock-forming order, magmatic source, tectonic setting and rock-forming process, combined with the achievements of regional rock-controlling structures and division of sublayer of crust, it is believed that Fenghuangshan rock body derives from the deep-seated alkalic basalt magma. The rock-forming process has undertaken sialic and calcareous assimilation and contamination of two different degrees. The rock-forming model belongs to the typical assimilation and fractional cryatalization mechanism.

Approaches to location prognosis of concealed ore deposits (bodies) of productive mines

This paper demonstrates the channels and methods for location prognosis of concealed ore deposits (bodies) in the deep-seated and surrounding districts of productive mines in accordance with their special features. The system frame map is built, from quick exploration in the field to the rapid building of a model indoors. The main research points of location prognosis are also discussed in the paper, which include: 1) integrating the location with the surrounding geological areas, microscopic with macroscopic; 2) analyzing and synthesizing all geological information of different levels, depths and aspects; 3) laying stress on mineralization series; 4) paying attention to the study of the distribution law of ore bodies; 5) introducing the theory of nonlinear dynamics of ore forming processes to ordinary static prognosis; 6) the necessity of the geophysical method in recovering information of concealed ore bodies; 7) the combination of all kinds of geology, geophysics, geochemistry and remote -sensing methods.

REE characteristics and genesis of alkaline-rich porphyry, Yunnan Province

The Yunnan Himalayan alkaline-rich porphyry occurs as a compound rockbelt and consists of calca-alkalic, alkaline and peralkaline intrusions. Its origin is in debate. The paper deals with its origin by studying rock’s REE and Sr isotope. Although the rocks are different in their REE contents varying from 77.53 µg/g to 1 798.3 µg/g, they have very similar features in REE parameters. On the triangalar diagram of REEs, the sample dots are concentrated on the end area of light REEs, representing a product of low-degree melting of upper mantle or lower crust materials. The initial 87Sr/86Sr values of rocks vary between 0.706 4 and 0.709 8, showing a feature of mantle-crust mixed source. Moreover, REEs show a logarithmic linear positive correlation between them. This type of correlation strongly supports the fractional-partial melting model. The result of geochemistry inversion shows that the source rock of alkaline-rich porphyry is plagioclase-bearing harzburgite and of mantle-crust mixed type. At the early state of melting, some crust components of the source rock were partially melted into intermediate-acidic magma; with the crust components consumed, the magma evolved to basic.

Genesis of the alkali-rich porphyries in Yunnan

The alkali-rich porphyries formed in the structural relaxation epoch of the Himalayan Movement. The tectonic setting and crustal structure in which the rocks formed and the compositional regionization feature of the rocks indicate that the magma formed inside the crust, which is further proved by REE. Sr and Pb isotope data. Combined the aforesaid data with the result of REE inversion, it is suggested as a new opinion that the alkali-rich porphyries were the remelting product of the mixture of mantle rocks intrusing into the crust with crustal material.

New evidences for the formation of granitic rocks by remelting of the sial crust in Southern Hunan

Comparatively analyzing 47 REE distribution data of the Southern Hunan geosynclinal arkose-silicarenite and various period granitic rocks and the results of their partially melting experiment series in company with the occurence and petrogeochemical features of various period granitic rocks, the authors suggest that all of the above-mentioned salic rocks can be partially melt to produce granitic magma.Comparatively analyzing 47 REE distribution data of the Southern Hunan geosynclinal arkose-silicarenite and various period granitic rocks and the results of their partially melting experiment series in company with the occurence and petrogeochemical features of various period granitic rocks, the authors suggest that all of the above-mentioned salic rocks can be partially melt to produce granitic magma.