Apparent Re–Os ages of some magmatic sulfide ore deposits are older than the zircon and baddeleyite U–Pb ages which are interpreted as the formation age of the host intrusions. The Jinchuan Ni–Cu–PGE deposit of China, the world's third largest, is such a case. We report apparent Re–Os isochron ages of 1117 ± 67 Ma, 1074 ± 120 Ma and 867 ± 75 Ma with initial 187Os/188Os ratios of 0.120 ± 0.012, 0.162 ±0.017 and 0.235 ± 0.027 for disseminated ores, sulfides from the disseminated ores and massive ores from Jinchuan, respectively. Using these data and Re–Os ages from the literature, we find that the oldest apparent Re–Os age and lowest initial Os isotope ratio are from disseminated ores which contain small amounts of sulfide minerals, the highest initial Os isotope ratios and youngest apparent Re–Os ages, consistent with the zircon and baddeleyite U–Pb ages, are from massive ores containing 90–100 modal% sulfide, and net-textured ores with about 25 modal% sulfides yield apparent Re–Os ages and initial Os ratios intermediate between those of the disseminated and massive ores.Because Os diffusion between sulfides is inhibited by the intervening silicates even at high temperatures, re-equilibration did not occur in the disseminated ore and the samples retained the Os ratios of the contaminated magma, leading to geologically meaningless ages that are older than the formation age of the rocks. While Os-bearing sulfide minerals and magnetite show low closure temperatures of Os diffusion and the sulfide minerals in the massive ore are closely connected with each other, facilitating fast diffusion of Os, re-equilibration of Os was achieved during cooling of the ore from about 850 °C after the segregation to about 400 °C. Thus, an age corresponding to the formation time and an elevated initial Os ratio were yielded by the massive ore. Os isotopes in the net-textured ore behave in the way intermediate between the disseminated and massive ores. Pb isotope data support the Os results. Disseminated ores have heterogeneous Pb isotope ratios whereas Pb in the massive ores is more uniform, consistent with Pb isotopic equilibration in the massive ores, but not in the disseminated ores. 相似文献
The results of a first systematic study of spatial distribution of different elements in surface soil over of the Kavadarci
region, Republic of Macedonia, known for its nickel industrial activity are reported. The investigated region (360 km2) is covered by a sampling grid of 2 × 2 km2; whereas the sampling grid of 1 × 1 km2 was applied in the urban zone and around the ferronickel smelter plant (117 km2). In total 344 soil samples from 172 locations were collected. At each sampling point soil samples were collected at two
depths, topsoil (0–5 cm) and bottom soil (20–30 cm). Inductively coupled plasma-mass spectrometry (ICP-MS) was applied for
the determination of 36 elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mn, Na, Mg, Mo, Ni, P,
Pb, S, Sb, Sc, Se, Sr, Th, Tl, Ti, U, V, W and Zn). Data analysis and construction of maps were performed using the Paradox
(ver. 9), Statistica (ver. 6.1), AutoDesk Map (ver. 2008) and Surfer (ver. 8.09) software. Four geogenic and three anthropogenic
geochemical associations were established. Within the research, natural and anthropogenic enrichment with heavy metals was
determined. Principally, the natural enrichment is related especially to Ni. Pollution by As, Cd, Co, Cr, Cu, Hg, Mo, Pb and
Zn is basically insignificant. 相似文献
The dynamics of desertification in the Horqin Sandy Land between 2000 and 2005 were analyzed using Landsat TM/ETM images and
the data-processing function of geographical information software. The results showed that the extent of desertified land
decreased at a rate of slightly more than 0.1 km2 year−1, from 22,423.1 km2 in 2000 to 22,422.4 km2 in 2005, indicating that desertification has been controlled in this area and that desert areas may be approaching a steady
state. The dynamics of desertification differed among land types. Desertification decreased most obviously in areas of previous
desert land. The area in which desertification was ameliorated was higher than the area that underwent further degradation,
but non-desertified land (113.3 km2) deteriorated at a rate of 22.7 km2 year−1 during this period. This significant change requires careful attention by managers in the study area. 相似文献
During the Maduo Earthquake (MDEq) (Mw 7.3), which occurred on 22 May 2021 in the northern Tibetan Plateau, coseismic surface ruptures, numerous land liquefaction instances and landslides, were triggered along the NW strike of the?~?160 km long aftershock zone. We performed three times emergency field surveys (22 May to 3 Jun., 28 Jun. to 14 Jul., 8–24 Oct., 2021) with unmanned aerial vehicle (UAV) orthophoto and digital elevation model (DEM) data. We found a discontinuous coseismic surface rupture zone along with loose sediment, severe sand liquefaction regions with an area of?~?103 km2 along the Yellow River and its tributaries. More than 23 coseismic landslides had been checked with relative small-size volume for limited local terrain relief. Three of those landslides had relatively small source areas and volumes and affected relatively large areas. We identified numerous tension cracks in and around the trailing edges, which could trigger more landslides in the future. Further detailed research into the occurrence of these three landslides will reveal the failure mechanism of the earthquake (shaking)–freeze–thaw effect–rainfall disaster chain. Here, we present basic information to aid the overall understanding of the preliminary characteristics of coseismic earthquake-triggered landslides, sand liquefaction, and possible follow-up disasters.