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Unusual minerals from harzburgite, the host rock of the Luobusa chromite deposit, Tibet

YANG JingSui,ZHANG ZhongMing,LI TianFu,LI ZhaoLi,REN XuFeng,XU XiangZhen,BA DengZhu,BAI WenJi,FENG QingSong,CHEN SongYong,RONG He,

岩石学报 , 2008,
Abstract: In recent years,ultrahigh pressure minerals,such as diamond and coesite,and other unusual minerals were discovered in chromitites of the Luobusa ophiolite in Tibet,and 4 new minerals have been approved by the CNMMN.These results have raised many questions:What are the occurrences of the diamonds,what is the source of their carbon and how were they formed? What is the origin of the chromites hosting the diamonds,and at what depth did they form? What is the genetic relationship between the diamonds and the ho...
Diamonds recovered from peridotite of the Purang ophiolite in the Yarlung-Zangbo suture of Tibet: A proposal for a new type of diamond occurrence.

YANG JingSui,XU XiangZhen,LI Yuan,LI JinYang,BA DengZhu,RONG He,ZHANG ZhongMing,

岩石学报 , 2011,
Abstract: After the discovery of diamonds and other unusual minerals in peridotites and chromitites of the Luobusa ophiolite, Tibet, it became important to determine if this was an isolated occurrence or if the same minerals occur in other ophiolites of the Yarlung-Zangbo suture zone. Here, we report the discovery of a similar collection of minerals in mantle peridotites of the Purang ophiolite, which lies in the westernmost part of the Yarlung-Zangbo suture, more than 1000km from the Luobusa massif. The Purang ophiolite consists mainly of harzburgite, lherzolite and dunite, probably of MOR type, which were modified in a SSZ environment. Many grains of diamond and some unusual minerals, such as moissanite, were recovered by standard mineral separation techniques from a 657kg sample of harzburgite. The presence of native Cr, Fe and Zn, together with the moissanite, indicates a strongly reducing environment. This discovery confirms that the Luobusa massif is not unique in the Yarlung-Zangbo suture. Based on the presence of similar minerals in the Ray-Iz ophiolite of the Polar Urals, and reports of diamonds in Alpine-type mantle peridotites, we suggest that diamonds and highly reduced minerals may be common in ophiolitic peridotites. These occurrences indicate a completely new environment for diamond formation, which can be regarded as ophiolite-type diamond, distinct from the other two well known types, i.e. kimberlitic diamonds and ultrahigh pressure metamorphic diamonds.
Explosion of Ultrahigh Pressure Minerals in the Mantle

BAI Wen-ji,YANG Jing-rui,FANG Qing-song,YAN Bing-gang,ZHANG Zhong-ming,

地球学报 , 2001,
Abstract: The microexplosion structure (cobweb structure) of ultrahigh pressure minerals was found for the first time in podiform chromitites within the mantle peridotite facies of Luobusa ophiolite along the Yarlung Zangbo suture zone. The explosion structures of high-energy silicate inclusions are commonly seen in thin sections. In explosion structure, chrome-spinel fragments are irregularly scattered in silicate minerals. With sharp edges and highly varied sizes, they are very unevenly distributed, showing distinct extention micro-brecciated structure. In addition, there are many tensional microfractures around the explosion silicate inclusions. It is inferred that, before explosion, the primary mantle minerals were hydrous magnesium silicate or magnesium-aluminium silicates. When such high-energy phase rose and passed the "water line" as a result of the action of mantle plume, explosion took place, accompanied by the release of water. The upward migration of large-sized high energy hydrous minerals may lead to deep-focus earthequakes.
Remote Sensing Monitoring on Mine of WorldView-2 Satellite: A Case Study of the Luobusa Area, Tibet

杨伟光, 郑有业, 刘婷, 王成松
YANG Weiguang
, ZHENG Youye, LIU Ting, WANG Chengsong

- , 2018,
Abstract: 摘要: 矿山遥感监测是近年来国土资源部门管理矿产资源开发、整顿和规范矿业秩序的一项重要的矿情调查工作。西藏罗布莎铬铁矿区是我国铬铁矿的主要产区,随着国民经济的快速发展,对铬铁矿石的开采力度和强度在逐年增大。为了更好地促进矿产经济及环境的可持续发展,选用WorldView-2遥感数据,首次深入分析了罗布莎矿山开发过程中不同地物遥感影像特征,建立了各类矿山地物的高空间分辨率遥感解译标志,通过遥感解译与野外查证工作,基本查明了研究区矿山开发状况和矿山地质生态环境现状,并对矿区开发现状与矿山环境进行了统计和分析,基于遥感矿山监测,给出了合理的矿山环境恢复建议。结果表明:WorldView-2作为高分辨率遥感影像,空间分辨率高,包含全色和8个多光谱波段,信息量丰富,解译精度高,在矿山遥感监测乃至更广范围的动态监测中应用可以取得很好的效果。
Abstract: Remote sensing monitoring of mine is an important survey work for exploitation of mineral resources, reorganization and standardization the order of mining industry by Ministry of Land and Resources in recent years. Chromitites mining area in Luobusa is the main chromitites production mine region in China.The exploitation intensity of mineral resources increases year by year due to the rapid development of national economy. In order to promote the sustainable development of the mining economy and environment, this article selects the WorldView-2 remote sensing data and profoundly analyzes remote sensing image characteristic of different surface features in the mine development process. Through field verification, we take advantage of WorldView-2 high spatial resolution remotely sensed data to establish the remote sensing interpretation keys of mine features so as to clarify development situation and ecological environment of this mineral area, and then conduct statistics and analysis of mining conditions and environment. Based on remote sensing monitoring of mine, reasonable suggestions about mine environmental recovery are given. Results show that WorldView-2 are with rich information and high precision of interpretation due to its high spatial resolution, panchromatic and eight multispectral bands, can obtain good effect in the remote sensing monitoring
Origin of different dunites in the Luobusa ophiolite, Tibet

LI JinYang,YANG JingSui,BA DengZhu,XU XiangZhen,MENG FanCong,LI TianFu,

岩石学报 , 2012,
Abstract: Three types of dunite occur in the Luobusa ophiolite, a thick layer of transition zone dunite, thin envelopes of dunite around podiform chromitites and small bands and lenses of dunite in the harzburgites, respectively. The transition zone dunite is about 700~1000m thick, and consists chiefly of high magnesium olivine (Fo93-95),low alumina and high magnesia clinopyroxene (Al2O3=0.47%~0.85%; Mg#=95~97),and high chrome and low magnesia Cr-spinel (Cr#=~77; Mg#=~51). Cr spinels in layers of disseminated chromite hosted in these dunites are similar in composition to those of the host rock but are slightly more magnesian (Mg#=~59) The dunite envelopes around the podiform chromitites are similar in composition to the transition zone dunite (olivine Fo92-94; Al2O3 in clinopyroxene <1% and Mg#=95~97; Cr# in Cr-spinel=71 and Mg#=52). The massive chromitites associated with the dunite envelopes have Cr#s averaging 79 and Mg#s averaging 68. The dunite lenses in harzburgite have olivine with somewhat lower Fo (91~92) and Cr-spinel with lower Cr#s (about 60), but clinopyroxene with higher Al2O3 (1.41%~1.71%). The mineral compositions in these lenses overlap those in the host harzburgite, with a gradual transition between them. The transition zone dunite in the Luobusa ophiolite is distinctly different from classic ultramafic cumulates, and most likely formed by reaction between tholeiitic basalt melt and mantle peridotite. Dunite lenses in the harzburgite may reflect either inhomogeneous partial melting of the host peridotites or in-situ melt-rock reaction. The dunite envelopes around the podiform chromitites are thought to have formed in the same way as the transition zone dunite, but the origin of the massive chromitites is not clear.
Platinum-Group Minerals in Chromitites of the Niquelandia Layered Intrusion (Central Goias, Brazil): Their Magmatic Origin and Low-Temperature Reworking during Serpentinization and Lateritic Weathering  [PDF]
Giorgio Garuti,Federica Zaccarini,Joaquin A. Proenza,Oskar A. R. Thalhammer,Nelson Angeli
Minerals , 2012, DOI: 10.3390/min2040365
Abstract: A variety of platinum-group-minerals (PGM) have been found to occur associated with the chromitite and dunite layers in the Niquelandia igneous complex. Two genetically distinct populations of PGM have been identified corresponding to phases crystallized at high temperatures (primary), and others formed or modified during post-magmatic serpentinization and lateritic weathering (secondary). Primary PGM have been found in moderately serpentinized chromitite and dunite, usually included in fresh chromite grains or partially oxidized interstitial sulfides. Due to topographically controlled lateritic weathering, the silicate rocks are totally transformed to a smectite-kaolinite-garnierite-amorphous silica assemblage, while the chromite is changed into a massive aggregate of a spinel phase having low-Mg and a low Fe 3+/Fe 2+ ratio, intimately associated with Ti-minerals, amorphous Fe-hydroxides, goethite, hematite and magnetite. The PGM in part survive alteration, and in part are corroded as a result of deep chemical weathering. Laurite is altered to Ru-oxides or re-crystallizes together with secondary Mg-ilmenite. Other PGM, especially the Pt-Fe alloys, re-precipitate within the altered chromite together with kaolinite and Fe-hydroxides. Textural evidence suggests that re-deposition of secondary PGM took place during chromite alteration, controlled by variation of the redox conditions on a microscopic scale.
Vaquero, M. P.
Grasas y Aceites , 1998,
Abstract: The possible changes in the mineral composition of food during frying could be the consequence of losses by leaching, or changes in concentrations caused by exchanges between the food and culinary fat of other compounds. The net result depends on the type of food, the frying fat used and the frying process. Moreover, the modifications that frying produces in other nutrients could indirectly affect the availability of dietary minerals. The most outstanding ones are those that can take place in the fat or in the protein. With respect to the interactions between frying oils and minerals, we have recent knowledge concerning the effects of consuming vegetable oils used in repeated fryings of potatoes without turnover, on the nutritive utilization of dietary minerals. The experiments have been carried out in pregnant and growing rats, which consumed diets containing, as a sole source of fat, the testing frying oils or unused oils. It seems that the consumption of various frying oils, with a polar compound content lower or close to the maximum limit of 25% accepted for human consumption, does not alter the absorption and metabolism of calcium, phosphorous, iron or copper. Magnesium absorption from diets containing frying oils tends to increase but the urinary excretion of this element increases, resulting imperceptible the variations in the magnesium balance. The urinary excretion of Zn also increased although its balance remained unchanged. Different studies referring to the effects of consuming fried fatty fish on mineral bioavailability will also be presented. On one hand, frying can cause structural changes in fish protein, which are associated with an increase in iron absorption and a decrease in body zinc retention. The nutritive utilization of other elements such as magnesium, calcium and copper seems to be unaffected. On the other hand; it has been described that an excess of fish fatty acids in the diet produces iron depletion, but when fatty fish is fried in olive oil the quality of the fish oil improves, enhancing the nutritive utilization of iron and other dietary minerals.
Chondritic osmium isotopic composition of late Archean convecting upper mantle: Evidence from Zunhua podiform chromitites, Hebei, North China
Qiongxia Xia,Xiachen Zhi,Jianghai Li,Xiongnan Huang
Chinese Science Bulletin , 2004, DOI: 10.1007/BF03183724
Abstract: Podiform chromite deposits are a characteristic feature of the mantle sequences of harzburgitic ophiolites. The chromites usually have very low Re and high Os contents, which makes it the most resistant phase remaining from the primary magmatic history of the ultramafic sections of ophiolites. The podiform chromite is one of the robust indicators of initial Os isotopic compositions of the ophiolites where podiform chromites were derived from, which provides strong evidence for the origin and evolution of oceanic lithosphere. The Re and Os contents and the Os isotopic compositions of seven podiform chromitites from Zunhua ophiolitic mélange belt, North China are reported in this study. The Re contents range from 0.019 to 0.128 ng/g, Os from 8.828 to 354.0 ng/g, and the187Os/l88Os ratio from 0.11003 to 0.11145. Three massive chromitites among the sample set have very high Os contents (> 300 ng/g), and their187Os/188Os ratios range from 0.11021 to 0.11030, averaging 0.11026±0.00005 (σ), equivalent to a γOs=~-0.12 ±0.06 at 2.6 Ga, which means that the Os isotopic composition of convecting upper mantle is chondritic in late Archean. It is the Os isotopic composition of podiform chromitites that are derived from the oldest ophiolite in the world till now.
Genesis of chromitites from Korydallos, Pindos Ophiolite Complex, Greece, based on spinel chemistry and PGE-mineralogy  [PDF]
Kapsiotis A N
Journal of Geosciences , 2013, DOI: 10.3190/jgeosci.133
Abstract: The Pindos Ophiolite Complex, located in northwestern Greece, hosts various chromite deposits of both metallurgical (high-Cr) and refractory (high-Al) type. In Korydallos are encountered both types of chromitites. These are podiform chromitites that have small dimensions and occur sub-concordantly to the hosting peridotites. The Cr-rich chromitites contain magnesiochromite with high Cr# [Cr/(Cr + Al): 0.65-0.68] and low platinum-group element (PGE) contents (294.1 ppb), whereas the Al-rich ones host spinel with low Cr# (0.44-0.48) and elevated total PGE grades (28830 ppb). The former display a nearly flat C1 normalized PGE-pattern, whereas the latter show a positively sloped normalized PGE-pattern. The in situ mineralogical investigation of the Cr-rich chromitites revealed a platinum-group mineral (PGM) assemblage dominated by small (≥ 3 μm) sperrylite, laurite and erlichmanite grains (determined by recalculated qualitative analytical data). Textural relations suggest crystallization under conditions of high fS2 and fAs and/or low T. The in concentrates mineralogical study of the Al-rich chromitites showed that the PGM assemblage that they host is dominated by Pd-Cu and Pd-Au-Cu alloys. The vast majority of these alloys is associated with abundant secondary BMS (base metal sulfides) and BMA (base metal alloys), thus confirming that a sulfide melt scavenged the PGE + Au of the silicate magma from which chromian spinel had already started to crystallize. Both assemblages were affected by an invasion of an oxidizing aqueous fluid in the investigated chromitites. Combined data indicate that the chromitites from the Korydallos area crystallized from a progressively differentiating MORB/IAT melt, produced in a small back-arc basin in a supra-subduction zone setting.
Geochemistry of Chromitites in Eastern Part of Neyriz Ophiolite Complex (Southern Iran)  [PDF]
Pedram Attarzadeh, Mehrdad Karimi, Mohammad Yazdi, Kamal Nouri Khankahdani
Open Journal of Geology (OJG) , 2017, DOI: 10.4236/ojg.2017.73015
Abstract: The Neyriz ophiolite complex is a part of NW-SE thrust belt (Late Cretaceous) of Iran, which is over the Arabian plate margin. The complex is mainly composed of the upper mantle rocks. Our research was focused on the eastern part of Neyriz ophiolite complex so called as “Dowlat Abad-Tang e Hana”. Mantle sequence of this ophiolitic complex is comprising predominantly of harzburgite and minor lherzolite, dunitc sheaths and chromite pods. Harzburgite is the most abundant ultramafic rock and is associated with the less dunite masses. The chromites are known with Cr# 42 to 76 and Mg# 73 to 89. There is a negative correlation between Cr#-Mg# which is one of the features of podiform chromites. The geochemistry of these chromites is consistent with the overall composition of podiform chromites in terms of Cr#, Mg#, the amounts of Cr2O3 (13.35% - 54.47%), Al2O3 (0.43% - 8%), MgO (13.25% - 38.56%), TiO2 (0.003% - 0.206%) as well as the correlations between various oxides and all of them are high chromium types.
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