酸化水与方解石石膏反应的模拟计算研究

利用水文地球化学模拟软件PHREEQIC对酸化水与方解石、石膏的反应进行了初步的模拟研究,从而了解不同酸度条件下的溶浸液对可溶矿物的溶蚀效果,对试验效果进行理论预测研究,提出了适合室内试验的溶浸液配方。     

桂北沙子江花岗岩型铀矿床碳、氧、硫同位素特征及其成因意义

测定了沙子江矿床及邻区矿床中与矿化密切有关的脉石矿物的稳定同位素,测知沙子江矿床方解石的δ13CPDB值为-2.8‰~-11.0‰,集中于-5‰~-9‰;表明矿化剂CO2主要来自地幔,混有少量有机质和沉积碳酸盐物质。δ13CPDB与δ18OSMOW呈显著的负相关关系,暗示流体去气(CO2)是方解石沉淀的主控因素。铀沉淀为多因素耦合作用的结果;去气作用导致成矿流体中碳酸铀酰络离子的解体,有利于铀的沉淀。S2-作为还原剂对铀沉淀也起了很大的作用。沙子江矿床黄铁矿的δ34SCDT值为-18.36‰~-8.92‰,可能主要来源于赋矿的花岗岩,而邻区孟公界和白毛冲矿床的δ34SCDT值为-30.51‰~-27.64‰,更多地继承了赋矿花岗岩源岩中沉积硫的特征。     

Carbon and Oxygen Isotope Compositions of Calcite and Rhodochrosite from Geothermal Exploratory Drills TH‐4 and TH‐6 near the Toyoha Deposit,Hokkaido, Japan

We studied calcite and rhodochrosite from exploratory drill cores (TH‐4 and TH‐6) near the Toyoha deposit, southwestern Hokkaido, Japan, from the aspect of stable isotope geochemistry, together with measuring the homogenization temperatures of fluid inclusions. The alteration observed in the drill cores is classified into four zones: ore mineralized zone, mixed‐layer minerals zone, kaolin minerals zone, and propylitic zone. Calcite is widespread in all the zones except for the kaolin minerals zone. The occurrence of rhodochrosite is restricted in the ore mineralized zone associated with Fe, Mn‐rich chlorite and sulfides, the mineral assemblage of which is basically equivalent to that in the Toyoha veins. The measured δ¹⁸O_SMOW and δ¹³C_PDB values of calcite scatter in the relatively narrow ranges from ?2 to 5‰ and from ?9 to ?5‰, respectively; those of rhodochrosite from 3 to 9‰ and from ?9 to ?5‰, excluding some data with large deviations. The variation of the isotopic compositions with temperature and depth could be explained by a mixing process between a heated surface meteoric water (100°C δ¹⁸O =?12‰, δ¹³C =?10‰) and a deep high temperature water (300°C, δ¹⁸O =?5‰, δ¹³C =?4‰). Boiling was less effective in isotopic fractionation than that of mixing. The plots of δ¹⁸O and δ¹³C indicate that the carbonates precipitated from H₂CO₃‐dominated fluids under the conditions of pH = 6–7 and T = 200–300°C. The sequential precipitation from calcite to rhodochrosite in a vein brought about the disequilibrium isotopic fractionation between the two minerals. The hydrothermal fluids circulated during the precipitation of carbonates in TH‐4 and TH‐6 are similar in origin to the ore‐forming fluids pertaining to the formation of veins in the Toyoha deposit.     

埋藏条件下方解石热力学平衡及其在塔河油田埋藏岩溶预测中的应用

方解石在成岩环境中的溶解度与地下水化学特征、温度等有着极为密切的关系。通过CaCO3溶解沉淀反应平衡以及地下水中的Ca2+活度可以确定不同温压的地下水条件下方解石的溶解趋势。地下水溶液的pH值和温度是方解石溶解度最直接的控制因素。方解石溶解趋势可以通过CaCO3电离反应的吉布斯自由能(ΔG)来判断:ΔG<0时,反应向溶解方向进行;ΔG>0时,反应向沉淀方向进行。根据方解石的水岩反应理论,对塔河油田34口井的奥陶系地层水进行了ΔG的统计计算。结果显示:塔河油田现今地下水条件有利于方解石的溶解,西部地区较东部溶解趋势强,北部地区溶解趋势相对较弱。这为定量了解塔河地区埋藏岩溶趋势及该地区的储层评价预测提供了理论依据。     

滇西北白秧坪多金属矿集区东矿带方解石REE地球化学特征及意义

方解石是白秧坪多金属矿集区东矿带矿石中的主要脉石矿物。不同产状矿体中方解石的REE地球化学特征研究表明,3个矿段成矿期方解石具有2种稀土模式:LREE(轻稀土元素)富集型和相对平坦型;前者表明成矿过程中没有LREE明显带出的迹象,残余热液继承了前期成矿热液的特征,而后者表明成矿过程中有LREE带出。不同类型矿体方解石中REE含量、有关参数和稀土配分模式等均变化较大,但在地球化学特征上具有连续变化规律,显示为同源不同阶段的产物。方解石为热液成因方解石,结合其他同位素的资料和矿区的地质背景,得出成矿流体以大气降水与围岩反应形成的热卤水为主、深部流体参与其成矿作用的观点。成矿过程中,由早到晚,成矿环境表现为还原向氧化环境变化。     

Calcite–graphite isotope thermometry in amphibolite facies marble, Bancroft, Ontario

This study presents calcite–graphite carbon isotope fractionations for 32 samples from marble in the northern Elzevir terrane of the Central Metasedimentary Belt, Grenville Province, southern Ontario, Canada. These results are compared with temperatures calculated by calcite–dolomite thermometry (15 samples), garnet–biotite thermometry (four samples) and garnet–hornblende thermometry (three samples). Δ_cal‐gr values vary regularly across the area from >6.5‰ in the south to 4.0‰ in the north, which corresponds to temperatures of 525 °C in the south to 650 °C in the north. Previous empirical calibration of the calcite–graphite thermometer agrees very well with calcite–dolomite, garnet–biotite and garnet–hornblende thermometry, whereas, theoretical calibrations compare less well with the independent thermometry. Isograds in marble based on the reactions rutile + calcite + quartz =titanite and tremolite + calcite + quartz = diopside, span temperatures of 525–600 °C and are consistent with calculated temperature–X(CO₂) relations. Results of this study compare favourably with large‐scale regional isotherms, however, local variation is greater than that revealed by large‐scale sampling strategies. It remains unclear whether the temperature–Δ_cal‐gr relationship observed in natural materials below 650 °C represents equilibrium fractionations or not, but the regularity and consistency apparent in this study demonstrate its utility for thermometry in amphibolite facies marble.     

Effect of anthropogenic CO2 on the pH and the saturation states of calcite and aragonite of seawater

Growth of phytoplankton, zooplankton and probably most other marine organisms as well, is likely to be affected by the pH of seawater. Growth of calcareous shells and skeletons is less likely to be affected by the saturation states of calcite and aragonite but the dissolution is. The increase of CO₂ in the oceans due to burning of fossil fuel and clearing of forests is decreasing the pH of seawater and the degrees of saturation for calcite and aragonite wordwide. This paper presents the results of the first attempt to estimate the vertical distribution of anthropogenic CO₂, and the decreases in pH and the degrees of saturation of calcite and aragonite in seawater near Taiwan. Most effects are very small except for the possible dissolution of aragonite on the upper continental slope starting around 2050 AD.     

Origin of double‐tower raft cones in hypogenic caves

In the present paper, we describe the genetic mechanism that causes the precipitation of raft cones in caves. These speleothems usually form in a hydrothermal and epiphreatic environment where dripwater, dripping repeatedly over the same spot, sinks calcite rafts that were floating on the water surface of a cave pool. In particular, the paper describes a new variety of raft cones that were recently discovered in the Paradise Chamber of the Sima de la Higuera Cave (Murcia, south‐eastern Spain) based on their morphological and morphometric characteristics. These speleothems, dubbed ‘double‐tower cones’, have a notch in the middle and look like two cones, one superimposed over the other. The genetic mechanism that gave rise to the double‐tower cones must include an intermediate stage of rapid calcite raft precipitation, caused by a drop in the water table and by changes in cave ventilation leading to greater carbon dioxide (CO₂) degassing and evaporation over the surface of the thermal lake where these speleothems formed. Calcite rafts were deposited in Paradise Chamber, completely covering many of the cones. Later, conditions for slower calcite raft precipitation were restored and some of the cones continued to grow at the same points. When the water table finally fell below the level of Paradise Chamber, the tower cones became exposed, as the incongruent deposits of calcite rafts were dissolved and mobilized to lower cave levels. Copyright © 2013 John Wiley & Sons, Ltd.     

含方解石铜矿石微生物氧化作用的实验研究

矿山固体废物中硫化物经微生物作用形成的酸性矿山排水及其引起的重金属污染是备受关注的环境问题,而岩石和矿石中的方解石能够影响酸性矿山排水的生成和迁移。为了考察方解石对硫化物-微生物氧化作用的影响,开展了系统的模拟实验,利用ICP-AES、XRD、XRF等分析手段,测定了实验溶液的pH值、Eh值、离子浓度和次生沉淀成分。结果表明,在无方解石或方解石含量低时,黄铜矿的微生物氧化过程中,pH值下降、Eh值上升,有多种重金属离子进入溶液,并生成大量黄钾铁矾、自然硫等次生沉淀。添加过量方解石能有效中和氧化过程产生的酸并能显著抑制氧化菌的活动。因此通过添加碳酸盐矿物的方法可使溶液pH调节至微碱性,降低微生物的活性、阻滞铜矿石的氧化,能够有效降低重金属的释放。     

Late Quaternary variations in calcium carbonate preservation of deep-sea sediments in the northern Cape Basin: results from a multiproxy approach

In this study, we test various parameters in deep-sea sediments (bulk sediment parameters and changes in microfossil abundances and preservation character) which are generally accepted as indicators of calcium carbonate dissolution. We investigate sediment material from station GeoB 1710-3 in the northern Cape Basin (eastern South Atlantic), 280 km away from the Namibian coast, well outside today’s coastal upwelling. As northern Benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr (Volbers et al., submitted), GeoB 1710-3 sediments reflect these changes in upwelling productivity. Results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity. Accordingly, these conventional proxy parameters misrepresent, to some extent, the extent of calcium carbonate dissolution. These results were verified by an independent dissolution proxy, the Globigerina bulloides dissolution index (BDX′) (Volbers and Henrich, submitted). The BDX′ is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr, with the exception of one pronounced dissolution event at early oxygen isotopic stage (OIS) 6.

The early OIS 6 is characterized by calcium carbonate contents, sand contents, and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr. At the same time, the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased, as are the rain ratio, the fragmentation index, and the BDX′. The sedimentary calcite lysocline rose above the core position and GeoB 1710-3 sediments were heavily altered, as attested to by the unusual accumulation of pellets, aggregates, sponge spicules, radiolaria, benthic foraminifera, and planktonic foraminiferal assemblages.

Solely the early OIS 6 dissolution event altered the coarse fraction intensely, and is therefore reflected by all conventional calcium carbonate preservation proxies and the BDX′. We attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes: (a) a prominent change in the deep-water mass distribution within the South Atlantic and (b) intense degradation of organic material within the sediment (preserved as maximum total organic carbon content) creating microenvironments favorable for calcium carbonate dissolution.