黄铁矿与沥青铀矿的共生条件及在沥青铀矿形成过程中所起作用的实验研究

高价铁与高价铀混合溶液在还原场中形成了共生的黄铁矿与沥青铀矿,该过程必须在弱酸性-中性-碱性介质中进行,其中在弱酸性至中性介质中易形成大的黄铁矿单晶。高价铀溶液流经黄铁矿矿区时,若在高温高压条件下,有新生的黄铁矿或白铁矿与沥青铀矿共生。黄铁矿还原六价铀形成沥青铀矿时,起还原作用的是二价硫。赤铁矿常与沥青铀矿共生,但它们是热液演化过程中不同阶段的产物,赤铁矿形成于体系氧逸度高的氧化环境,沥青铀矿形成于体系氧逸度低的还原环境,赤铁矿形成于沥青铀矿之前。     

香格里拉县红牛矽卡岩型铜矿

“三江成矿带”内的红牛铜矿,赋存于大理岩边部矽卡岩化蚀变带及角岩体中。赋矿地层为曲嘎寺组第二段。对矿石结构、构造及矿石矿物成分、共生伴生关系等进行研究,明确找矿标志。     

Origin and evolution of the Steamboat Springs siliceous sinter deposit, Nevada, U.S.A.

Siliceous hot spring deposits from Steamboat Springs, Nevada, U.S.A., record a complex interplay of multiple, changing, primary environmental conditions, fluid overprinting and diagenesis. Consequently these deposits reflect dynamic geologic and geothermal processes. Two surface sinters were examined—the high terrace, and the distal apron-slope, as well as 13.11 m (43 ft) of core material from drill hole SNLG 87-29. The high terrace sinter consists of vitreous and massive-mottled silica horizons, while the distal deposit and core comprise dominantly porous, indurated fragmental sinters. Collectively, the three sinter deposits archive a complete sequence of silica phase diagenetic minerals from opal-A to quartz. X-ray powder diffraction analyses and infrared spectroscopy of the sinters indicate that the distal apron-slope consists of opal-A and opal-A/CT mineralogy; the core yielded opal-A/CT and opal-CT with minor opal-A; and the high terrace constitutes opal-C, moganite, and quartz. Mineralogical maturation of the deposit produced alternating nano–micro–nano-sized silica particle changes. Based on filament diameters of microbial fossils preserved within the sinter, discharging thermal outflows fluctuated between low-temperatures (< 35 °C, coarse filaments) and mid-temperatures ( 35–60 °C, fine filaments). Despite transformation to quartz, primary coarse and fine filaments were preserved in the high terrace sinter. AMS ¹⁴C dating of pollen from three horizons within core SNLG 87-29, from depths of 8.13 to 8.21 m (26′8″ to 26′11″), 10.13 to 10.21 m (33′3″ to 33′6″), and 14.81 to 14.88 m (48′7″ to 48′10″), yielded dates of 8684 ± 64 years, 11,493 ± 70 years and 6283 ±60 years, respectively. In the upper section of the core, the stratigraphically out-of-sequence age likely reflects physical mixing of younger sinter with quartzose sinter fragments derived from the high terrace. Within single horizons, mineralogical and morphological components of the sinter matrix were spatially patchy. Overall, the deposit was modified by sub-surface flow of alkali-chloride thermal fluids depositing a second generation of silica, and periodically, by acidic steam condensate formed during periods when the water table was low. Local faulting produced considerable fracturing of the sinter. Hence, the Steamboat Springs sinter experienced a complex history of primary and secondary hydrothermal, geologic and diagenetic events, and their inter-relationships and effects are locked within the physical, chemical and biological signatures of the deposit.     

Geology and ore genesis of the late Paleozoic Heijianshan Fe oxide–Cu (–Au) deposit in the Eastern Tianshan,NW China

The Heijianshan Fe–Cu (–Au) deposit, located in the Aqishan-Yamansu belt of the Eastern Tianshan (NW China), is hosted in the mafic–intermediate volcanic and mafic–felsic volcaniclastic rocks of the Upper Carboniferous Matoutan Formation. Based on the pervasive alteration, mineral assemblages and crosscutting relationships of veins, six magmatic–hydrothermal stages have been established, including epidote alteration (Stage I), magnetite mineralization (Stage II), pyrite alteration (Stage III), Cu (–Au) mineralization (Stage IV), late veins (Stage V) and supergene alteration (Stage VI). The Stage I epidote–calcite–tourmaline–sericite alteration assemblage indicates a pre-mineralization Ca–Mg alteration event. Stage II Fe and Stage IV Cu (–Au) mineralization stages at Heijianshan can be clearly distinguished from alteration, mineral assemblages, and nature and sources of ore-forming fluids.Homogenization temperatures of primary fluid inclusions in quartz and calcite from Stage I (189–370 °C), II (301–536 °C), III (119–262 °C) and V (46–198 °C) suggest that fluid incursion and mixing probably occurred during Stage I to II and Stage V, respectively. The Stage II magmatic–hydrothermal-derived Fe mineralization fluids were characterized by high temperature (>300 °C), medium–high salinity (21.2–56.0 wt% NaCl equiv.) and being Na–Ca–Mg–Fe-dominated. These fluids were overprinted by the external low temperature (<300 °C), medium–high salinity (19.0–34.7 wt% NaCl equiv.) and Ca–Mg-dominated basinal brines that were responsible for the subsequent pyrite alteration and Cu (–Au) mineralization, as supported by quartz CL images and H–O isotopes. Furthermore, in-situ sulfur isotopes also indicate that the sulfur sources vary in different stages, viz., Stage II (magmatic–hydrothermal), III (basinal brine-related) and IV (magmatic–hydrothermal). Stage II disseminated pyrite has δ³⁴S_fluid values of 1.7–4.3‰, comparable with sulfur from magmatic reservoirs. δ³⁴S_fluid values (24.3–29.3‰) of Stage III Type A pyrite (coexists with hematite) probably indicate external basinal brine involvement, consistent with the analytical results of fluid inclusions. With the basinal brines further interacting with volcanic/volcaniclastic rocks of the Carboniferous Matoutan Formation, Stage III Type B pyrite–chalcopyrite–pyrrhotite assemblage (with low δ³⁴S_fluid values of 4.6–10.0‰) may have formed at low fO₂ and temperature (119–262 °C). The continuous basinal brine–volcanic/volcaniclastic rock interactions during the basin inversion (∼325–300 Ma) may have leached sulfur and copper from the rocks, yielding magmatic-like δ³⁴S_fluid values (1.5–4.1‰). Such fluids may have altered pyrite and precipitated chalcopyrite with minor Au in Stage IV. Eventually, the Stage V low temperature (∼160 °C) and low salinity meteoric water may have percolated into the ore-forming fluid system and formed late-hydrothermal veins.The similar alteration and mineralization paragenetic sequences, ore-forming fluid sources and evolution, and tectonic settings of the Heijianshan deposit to the Mesozoic Central Andean IOCG deposits indicate that the former is probably the first identified Paleozoic IOCG-like deposit in the Central Asian Orogenic Belt.     

共生于同一金刚石中的超镁铁岩与榴辉岩矿物包裹体

辽南５０号金伯利岩管金刚石的包裹体类型一直被认为是以超镁铁岩组合为主。最近，在同一岩管中发现一颗金刚石中有两种组合类型矿物共生：橄榄石，为超镁铁岩型；石榴石，绿辉石，为榴辉岩型组合。化学成分分析还表明，同一矿物的不同颗粒化学成分没有明显变化。根据石榴石与绿辉石的共生组合关系，钙、镁和铁之间的交换，计算其平衡温度为１２０３℃，压力为５×１０￣９Ｐａ。超镁铁岩与榴辉岩包裹体共生，表明该金刚石成生环境的复杂性。很可能是地幔动力学过程或者是幔源岩浆多期多相导致金刚石成生环境的迅速变化。     

Textures, paragenesis and wall-rock alteration of lode-gold deposits in the Charters Towers district, north Queensland: implications for the conditions of ore formation

Ore deposits of the Charters Towers Goldfield (CTGF) are mainly hosted by fault-fill veins. Extensional (∼8% of all veins) and stockwork-like (∼3%) veins are less common and of little economic significance. Crosscutting relationships and published structural and geochronological data indicate a Late Silurian to Early Devonian timing of gold mineralization, coincident with regional shortening (D₄) and I-type magmatism. Paragenetic relationships, which are uniform in veins everywhere within the CTGF, suggest that vein formation commenced with the deposition of large volumes of buck quartz (stage I), followed by buck and comb quartz, and significant pyrite and arsenopyrite precipitation (stage II). Gold was introduced during stage III, after earlier sphalerite and coincident with galena and chalcopyrite. Narrow, discontinuous calcite veins of stage IV mark the waning of gold-related hydrothermal activity or a later unrelated episode. Ore zones within the veins are everywhere composed of comb and/or gray quartz, calcite and/or ankerite and bands or clusters of fractured pyrite that are spatially associated with galena, sphalerite or chalcopyrite. Low-grade or barren vein sections, on the other hand, are mainly composed of milky buck quartz with little evidence for modification, overprinting or interaction with later fluids. Gold-related hydrothermal wall-rock alteration is symmetrically zoned, displaying proximal sericite–ankerite and distal epidote–chlorite–hematite assemblages that may be taken to imply wall-rock interaction with near neutral fluids (pH 5–6). Isocon plots assuming immobile Al, P, Ti, Y and Zr consistently indicate As, K, Pb, S and Zn enrichment and Na, Si and Sr depletion in altered wall-rock specimens relative to the least altered rocks. Alteration assemblages, quartz textures, fault rocks and published fluid inclusion and stable isotope data imply that the veins were formed under conditions of episodic fluid overpressuring (∼0.9–3.8 kbar), at a depth of ∼7 km and a temperature of ∼310°C. The published fluid inclusion data also imply that gold precipitation may have been brought about by fluid mixing. However, physi- and chemisorption of gold complexes onto sulfide surfaces may have been important depositional processes and controls on gold enrichment at the millimeter to centimeter scale, given that most gold particles are attached to the surfaces of pyrite crystals of stage II or to etch-pits and fracture surfaces within the earlier pyrite.     

云南光明铁多金属矿与矽卡岩选择性成矿关系

详细论述两种不同类型石榴石矽卡岩和透辉石矽卡岩与铁矿及其共生、伴生矿铜、铅、锌、锡等的富集规律,总结出铁多金属矿与矽卡岩之间的选择性富集关系。     

斑岩铜矿床成矿流体演化:中甸普朗铜矿床蚀变矿物学与热力学模拟

不同阶段热液蚀变矿物的组成是水岩反应过程和成矿流体演化的地球化学"指纹"。三江特提斯义敦岛弧南缘的普朗超大型斑岩铜矿床形成于晚三叠世甘孜-理塘洋西向俯冲的岛弧环境,但具有不同于典型斑岩铜矿的蚀变-矿化分带特征:即在早期钾硅酸盐化蚀变带内常可见晚期脉状(沿裂隙分布的细脉状)青磐岩化或沿破碎带边部发育的绢英岩化,且主要在青磐岩化蚀变带内发育铜(-钼)矿化。为此,本研究选取普朗矿床含矿石英二长斑岩(QMP)中热液黑云母及绿泥石进行矿物产状、共生组合和世代划分研究,并针对不同产状的绿泥石开展电子探针分析研究,以探讨其形成的物理化学条件,并结合热力学模拟结果反演成矿流体演化轨迹。不同于岩浆黑云母(Bt-1)的锯齿状边缘及内部发育磷灰石包体特征,普朗铜矿热液黑云母(Bt-2)多为片状且解理发育、沿其边缘或裂隙多被绿泥石交代。青磐岩化带内发育有两类产状明显不同的绿泥石,即由黑云母蚀变而成的片状绿泥石(Chl-1)和蠕虫状绿泥石(Chl-2),且后者多与黄铜矿、黄铁矿、磁黄铁矿及辉钼矿伴生。电子探针分析结果显示两类绿泥石均为富Mg的三八面体类绿泥石,且具有相似的主量元素组成。石英二长斑岩中Bt-2型黑云母形成温度范围为305-336℃(平均值为321℃),氧逸度位于NNO(Ni-NiO)缓冲线与HM(Fe_2O_3-Fe_3O_4)缓冲线之间。Chl-1和Chl-2型绿泥石形成温度分别为284～347℃(平均值为316℃)和278～328℃之间(平均值为310℃)。Chl-1和Chl-2的Log f_(O_2)分别在-42.7--37.2(平均值-39.8;ΔFMQ=-5.7)和-41.8～-38.4之间(平均值-40.0;ΔFMQ=-5.5),对应的Log f_(S_2)在-14.9～-12.1(平均值-13.5)和-14.5～-12.7之间(平均值-13.6)。不同蚀变阶段矿物组合特征及热力学模拟结果表明,在早期高温的钾硅酸盐化阶段含矿流体具有高氧逸度、中性特征(ΔFMQ=2,pH=7),在中温青磐岩化阶段具有低氧逸度、酸性特征(ΔFMQ=0,pH=4.8),在晚期绢英岩化阶段pH值变化不大而氧逸度略有升高。综合上述矿化-蚀变时空结构和热力学模拟结果,本研究显示普朗铜矿床强烈的蚀变叠加与青磐岩化矿化现象与围岩碳质地层随着大气水沿断裂带渗入到岩浆热液系统中有关。还原性物质伴随着大气水的渗入破坏了原始岩浆热液系统化学平衡,可能是导致普朗铜矿蚀变叠加及在青磐岩化阶段铜等成矿物质大规模聚集的关键原因之一。     

大理州漾濞塔盘山锑-金矿床

以往工作对象是锑矿,伴生、独立存在的金矿未被重视。本文认为塔盘山锑、金矿床是富有机质的盆地热卤水以及古海水与深大断裂引起的韧性剪切带有关的低温变质热液改造矿床,有望找到中-大型金矿床。     

南襄盆地泌阳凹陷油、碱共生的地质条件

南(阳)襄(樊)盆地泌阳凹陷是一个油、碱共生的蒸发岩盆地,已探明规模石油与天然碱(NaHCO₃和Na₂CO₃·3NaHCO₃)地质储量。原油分为成熟油和未熟(低熟)油,成熟油储集于碎屑岩中,未熟(低熟)油储集于白云岩的裂缝和孔洞之中,而天然碱矿的围岩就是白云岩(裂缝和孔洞中也有天然碱赋存)。其地质特征与美国绿河盆地和犹英塔盆地十分相似,油碱共生受控于大地构造背景、古地貌、古地理、古气候、古沉积环境和物质来源等地质条件。