The mafic-ultramafic complex near Finero (Ivrea-Verbano Zone), I. Chemistry of MORB-like magmas     

Meihua Lu  Albrecht W. Hofmann  Maurizio Mazzucchelli  Giorgio Rivalenti 《Chemical Geology》1997,140(3-4):207-222

Geochemical data are presented for the meta-igneous, mafic-ultramafic complex near Finero. This complex is in contact with a phlogopite-bearing mantle peridotite and is subdivided into the Internal Gabbro unit, the Amphibole Peridotite unit, and the External Gabbro unit. The Internal Gabbro and the Amphibole Peridotite units consist of coarse-grained, chemically heterogeneous cumulates, whereas the External Gabbro unit is generally massive, chemically more uniform and approximately representative of the residual melt with MgO contents between 6.6 and 9.1% and Mg numbers between 38 and 58. Both whole-rock and mineral contents of Ni and Cr are significantly higher (at similar Mg numbers) in the Amphibole Peridotite unit than in the Internal Gabbro unit. The most straightforward interpretation of this is that the Amphibole Peridotite unit accumulated after the influx of fresh mafic (or ultramafic) magma into the magma chamber. Major-element chemical trends are continuous from the Amphibole Peridotite unit to the External Gabbro unit and are consistent with closed-system fractionation with no further addition of magma or contamination by wall or roof rock assimilation. In the External Gabbro unit, total FeO and TiO₂ contents are strongly correlated with each other (and with P₂O₅ and Zr) and reach values as high as 19 and 4%, respectively, indicating an advanced degree of crystal fractionation along a tholeftic trend. The External Gabbro samples have generally smooth normalized trace element patterns, which are consistent with being representative of a liquid composition. The residual nature of the External Gabbro magma is also indicated by negative Eu and Sr anomalies, clear evidence for prior feldspar fractionation. REE patterns are otherwise indistinguishable from N-type MORB, but Th and U are significantly more depleted than in MORB. This Th and U depletion is similar to that found in olivine basalts and picrites on Iceland and Hawaii; its origin is not well understood. No evidence is seen for any assimilation of crystal material, in sharp contrast with the situation of the igneous complex in Val Sesia near Balmuccia, where the magma composition is dominated by assimilation of crust. We suggest that the heat provided by at most two injections of magma near Finero was insufficient to induce crystal anatexis, in contrast with the excess heat supplied by multiple magma injections at Balmuccia.  相似文献   

Mineral inclusions in diamonds from the Sputnik kimberlite pipe, Yakutia   总被引：9，自引：0，他引：9  

N. V. Sobolev  F. V. Kaminsky  W. L. Griffin  E. S. Yefimova  T. T. Win  C. G. Ryan  A. I. Botkunov 《Lithos》1997,39(3-4):135-157

The Sputnik kimberlite pipe is a small “satellite” of the larger Mir pipe in central Yakutia (Sakha), Russia. Study of 38 large diamonds (0.7-4.9 carats) showed that nine contain inclusions of the eclogitic paragenesis, while the remainder contain inclusions of the peridotitic paragenesis, or of uncertain paragenesis. The peridotitic inclusion suite comprises olivine, enstatite, Cr-diopside, chromite, Cr-pyrope garnet (both lherzolitic and harzburgitic), ilmenite, Ni-rich sulfide and a Ti-Cr-Fe-Mg-Sr-K phase of the lindsleyite-mathiasite (LIMA) series. The eclogitic inclusion suite comprises omphacite, garnet, Ni-poor sulfide, phlogopite and rutile. Peridotitic ilmenite inclusions have high Mg, Cr and Ni contents and high Nb/Zr ratios; they may be related to metasomatic ilmenites known from peridotite xenoliths in kimberlite. Eclogitic phlogopite is intergrown with omphacite, coexists with garnet, and has an unusually high TiO₂ content. Comparison with inclusions in diamonds from Mir shows general similarities, but differences in details of trace-element patterns. Large compositional variations among inclusions of one phase (olivine, garnet, chromite) within single diamonds indicate that the chemical environment of diamond crystallisation changed rapidly relative to diamond growth rates in many cases. P-T conditions of formation were calculated from multiphase inclusions and from trace element geothermobarometry of single inclusions. The geotherm at the time of diamond formation was near a 35 mW/m² conductive model; that is indistinguishable from the Paleozoic geotherm derived by studies of xenoliths and concentrate minerals from Mir. A range of Ni temperatures between garnet inclusions in single diamonds from both Mir and Sputnik suggests that many of the diamonds grew during thermal events affecting a relatively narrow depth range of the lithosphere, within the diamond stability field. The minor differences between inclusions in Mir and Sputnik may reflect lateral heterogeneity in the upper mantle.  相似文献   

Whole-rock and sulfide lead-isotope data from the hydrothermal JADE field in the Okinawa back-arc trough   总被引：7，自引：0，他引：7  

P. Halbach  W. Hansmann  V. Köppel  B. Pracejus 《Mineralium Deposita》1997,32(1):70-78

The mineralization of the active hydrothermal JADE field resembles in many aspects the Kuroko-type mineralization. The JADE field is located in a back-arc graben and is associated with a bimodal volcanism. Lead isotope data from igneous rocks, sediments, and ores further emphasize the similarities with the Kuroko ores and suggest that both sediments and volcanic rocks contributed comparable amounts of lead to the deposit. When compared to the sediments, a much larger volume of volcanic rocks must have contributed lead to the deposit, because of the considerably lower lead concentration of volcanic rocks. In contrast to the crustal type lead of the JADE field and the Kuroko-type sulfide deposits the lead isotope signatures of VMS-type deposits at mid-ocean ridges is distinctly different. In the absence of a sedimentary cover it reflects the composition of the mantle source, whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even be completely dominated by the latter. Received: 5 October 1995 / Accepted: 10 May 1996  相似文献   

Streambank fish-shelter structures help stabilize tributary streams in Wisconsin     

Stanley W. Trimble 《Environmental Geology》1997,32(3):230-234

 A significant proportion of stream sediment yield in North America comes from stream channel and bank erosion. One method used for stream stabilization is the bank installation of timber and stone fish-shelter structures, but there is little evidence for their potential effectiveness. Nine to nineteen years of precise survey data from Coon Creek, Wisconsin, however, show that fish structures enhance sediment deposition along the stream and may retard lateral migration of channels. Such structures have greater utility for sediment control when streams are eroding away a high bank and replacing it with a lower bank. Received: 18 October 1996 · Accepted: 4 February 1997  相似文献   

Environmental and legal aspects of karst areas   总被引：3，自引：0，他引：3  

P. E. LaMoreaux  W. J. Powell  H. E. LeGrand 《Environmental Geology》1997,29(1-2):23-36

 Environmental impacts on karst settings are common as they are more sensitive than those of other rock terrains. Regulatory procedures that are effective in other rock terrains are not necessarily applicable to karst settings. Development and exploitation by man that affect the karst hydrology regime can trigger catastrophic events and result in numerous legal actions where the effects of changes go beyond property boundaries. A great variety of regulations and examples of litigation exist for karst areas. Received: 25 October 1994 · Accepted: 17 October 1995  相似文献   

Radiometric characteristics of heavy mineral deposits along the west coast of South Africa     

W. G. Macdonald  A. Rozendaal  R. J. de Meijer 《Mineralium Deposita》1997,32(4):371-381

During the last decade, exploration and mining of modern-Tertiary heavy mineral beach and raised beach sands along the west coast of South Africa has developed into a major industry. High resolution radiometric techniques have demonstrated their use as a quantitative indicator of total heavy mineral concentration (THM) and also have the ability to discriminate between sediments derived from different provenance terrains. Results indicate that it is possible to calculate the total heavy mineral concentration from high resolution radiometric measurements, but the ability to quantify the concentration of individual mineral fractions, such as ilmenite, requires further refinement of the method. Radiometric characteristics of the light mineral fraction made it possible to distinguish between sediments from mixed marine-aeolian palaeoplacers and active present beach placers. The effects of in situ alteration of the ilmenite fraction in the palaeoplacers were also reflected by subtle contrasts in the radiometric character of the deposits. Furthermore, the uniform radiometric character of the sample population indicates a common provenance for the heavy mineral suite and supports previous results which indicate the metamorphites of the mid-Proterozoic Namaqua Province as the primary source terrain. The high resolution radiometric techniques discussed offer a broad spectrum of applications in sedimentology and have the potential to aid heavy mineral exploration. With further refinement it can possibly be used quantitatively in grade control during mining and beneficiation of heavy mineral deposits. Received: 19 July 1996 / Accepted: 7 January 1997  相似文献   

Automated AF-demagnetization on the 2G-Enterprises through-bore,cryogenic magnetometer     

Giddings  John W.  Klootwijk  Chris  Rees  John  Groenewoud  Adrian 《Geologie en Mijnbouw》1997,76(1-2):35-44

Since the early sixties, alternating field demagnetization (AFD) has been a standard laboratory technique for demagnetizing rocks to expose the multicomponent structure of their natural remanent magnetization (NRM). In the majority of AFD implementations, however, the procedure remains as labour-intensive as ever. The implementation that we have developed at the Australian Geological Survey Organisation, automates the procedure for AFD based on the static method, and results in significant productivity and efficiency gains without compromising data quality. A properly formulated procedure for static AFD may be the only method of retrieving higher-coercivity components of natural remanence in samples prone to developing gyroremanence at higher alternating fields (AFs). Our AFD environment comprises: a 2G-Enterprises through-bore, cryogenic magnetometer; 2G AF-coils and control equipment; and personal computer software, developed by us, to control all procedural aspects for a complete AFD of a sample including, importantly, a counteracting procedure to neutralize the effects of gyroremanence build-up at higher AFs. With our system, AFD of 8 samples/day, each of 20+ steps, requires only 20 min of user attention compared with a full day for conventional systems.  相似文献   

Geotechnical Hazards Associated with Desert Environment     

Shehata  W.M.  Amin  A.A. 《Natural Hazards》1997,16(1):81-95

The aridity of the Arabian Peninsula's deserts ranges between arid to hyperarid with hot dry climate, scarce precipitation and sparse vegetation. These harsh environmental conditions enhance some geomorphologic processes more than others, cause specific geotechnical problems, and increase desertification.From west to east, the general physiography of Saudi Arabia shows the Red Sea coastal plains and the escarpment foothills called Tihama followed by the Arabian Shield mountains, the Arabian Shelf plateau and finally the Arabian Gulf coastal plains. Sand moves by wind either as drifting sand or migrating dunes in four major sand seas, over the Arabian Shelf, and in the inter-mountain valleys, in the Arabian Shield causing problems of erosion and deposition. Human activities in the deserts may cause more instability to the sand bodies, enlarging the magnitude of the problem. Fine silty soil particles also move by wind, depositing loess mainly in selected areas downwind in the Tihama. These loess deposits subside and may form earth fissures by the process of hydrocompaction upon wetting. The addition of water can be either natural through storms or man-made through human agricultural or civil activities. Extensive sabkhas exist along the coastal plains of both the Red Sea and Arabian Gulf. The sabkha soil may also heave by salt re-crystallization or collapse by wetting. The shallow groundwater brines present in sabkhas also attack and corrode civil structures. Urbanization and excessive groundwater pumping may also deplete the fresh groundwater resources and may cause subsidence, ground fissuring and surface faulting as observed in some locations in the Arabian Shield. Although the average annual precipitation is very low, rain usually falls in the form of torrential storms, collected by dry valley basins and causing floods to unprotected downstream areas on the coastal plains of the Red Sea.The desert environment, being a fragile echo system, needs to be treated with care. Intercommunications between different national and international agencies and education of the layman should help to keep the system balanced and reduce the resulting environmental hazards. In addition, any suggested remedial measures should be planned with nature and engineered with natural materials.  相似文献   

ZP-1型钻杆疲劳试验台          下载免费PDF全文

刘峰  宋志彬  杨大根  王年友 《探矿工程》1997,(4):25-27

简述了ＺＰ－１型钻杆疲劳试验台的试验原理、主要技术性能参数和设计指导思想，并着重介绍了试验台机械传动系统和加载系统的组成、设计要点及试验台的试验情况。  相似文献   

Multi-phase water-rhyolite interaction and ore fluid generation at Aljustrel, Portugal     

F. J. A. S. Barriga  W. S. Fyfe 《Mineralium Deposita》1997,33(1-2):188-207

Detailed study of the Aljustrel volcanic rocks, through petrography, mineral chemistry, whole-rock geochemistry, and previously published stable isotope data, show that the rocks experienced extreme metasomatism. The metasomatic phenomena presented are explained accurately by a sea-water convective model. The evolution of the sea-water-derived fluid as it progresses downwards through the rocks is evident, from cold, oxidising, Mg-bearing, to hot, reducing, Mg-free, and enriched in Si, Fe, Cu, Zn. Several lines of evidence (feldspar mineralogy, paragenetic relations between regional and ore-zone alteration, and stable isotope data) show that the temperature of the hydrothermal circulation increased through time, and that the water-to-rock ratio evolved from very high to low values. According to our data, about 30 ppm Cu and some 100 ppm Zn were removed from the Aljustrel Volcanics. This implies, for both metals, the same amount of leached rock to produce the 2 Mt Cu and 6 Mt Zn contained in the massive sulphide deposits of the Aljustrel area. With regard to Fe, about 1% was on average removed from the rocks, producing enough metal to account for all the Fe in the MS deposits and overlying chemical sediments. This study documents semi-quantitatively the provenance of the main metals in major massive sulphide deposits via sea water leaching of the immediate host rocks.

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Resumen (translated by E. Pascual) Un estudio detallado de las rocas volcánicas de Aljustrel, mediante petrografia, química mineral, geoquímica de roca total y datos de isótopos estables previamente publicados muestra que estas rocas han sufrido metasomatismo en grado extremo. Los fenómenos metasomáticos presentados se explican con precisión mediante un modelo convectivo con agua de mar. Es evidente la evolución del fluido derivado del agua de mar conforme progresa en profundidad a través de las rocas, desde un fluido frío, oxidante y con magnesio a otro reductor, sin magnesio y enriquecido en Si, Fe, Cu y Zn. Varias líneas de evidencia (mineralogía de los feldespatos, relaciones paragenéticas entre la alteración regional y de las zonas mineralizadas, isótopos estables) muestran que la temperatura y la circulación hidrotermal se incrementaron con el tiempo y que la relación agua-roca evolucionó de valores muy altos a bajos. De acuerdo con nuestros datos, de las rocas volcánicas de Aljustrel se han extraído unas 30 ppm de Cu y unas 100 ppm de Zn. Esto implica, para ambos metales, que la misma roca lixiviada ha producido los 2 Mt de Cu y los 6 Mt de Zn contenidos en los depósitos de sulfuros masivos del área de Aljustrel. En cuanto al Fe, una media de alrededor de 1% fue extraída de las rocas, produciendo metal suficiente para explicar todo el Fe de los depósitos de sulfuros masivos y de los sedimentos químicos suprayacentes. Este estudio documenta de forma semicuantitativa la procedencia de los principales metales en depósitos mayores de sulfuros masivos, mediante lixiviado por agua de mar de sus rocas huéspedes inmediatas.

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Received: 1 February 1997 / Accepted: 30 July 1997  相似文献