The thermodynamic properties of radium

The enthalpy, Gibbs free energy, and entropies of aqueous radium species and radium solids have been evaluated from empirical data, or estimated when necessary for 25°C and 1 bar. Estimates were based on such approaches as extrapolation of the thermodynamic properties of Ca, Sr, and Ba complexes and solids plotted against cationic radii and charge to radius functions, and the use of the Fuoss or electrostatic mathematical models of ion pair formation (Langmuir, 1979). Resultant log K (assoc) and ΔH⁰ (assoc) (kcal/mol) values are: for RaOH⁺ 0.5 and 1.1; RaCl⁺ ?0.10 and 0.50; RaCO⁰₃ 2.5 and 1.07; and RaSO⁰₄ 2.75 and 1.3. Log Ksp and ΔH⁰ (dissoc) (kcal/mol) values for RaCO₃(c) and RaSO₄(c) are ?8.3 and ?2.8, and ?10.26 and ?9.4, respectively.Trace Ra solid solution in salts of Pb and of the lighter alkaline earths, has been appraised based on published distribution coefficient (D) data, where D ～- (mM²⁺)(N_RaX)/(mRa²⁺)(N_MX) (m and N are the aqueous molality and mole fraction of Ra and cation M in salt X, respectively. The empirical solid solution data have been used to derive both enthalpies and Gibbs free energies of solid solution of trace Ra in sulfate and carbonate minerals up to 100°C. Results show that in every case D values decrease with increasing temperature. Among the sulfate and carbonate minerals, D values decrease for the following minerals in the order: anhydrite > celestite > anglesite > barite > aragonite > strontianite > witherite > cerussite.     

Origin and history of waters associated with coalbed methane: I, Cl, and stable isotope results from the Fruitland Formation, CO and NM

The Fruitland Formation of the San Juan Basin was deposited during the late Cretaceous and is associated with significant reservoirs of coalbed methane (CBM). The purpose of this study is to determine the origin and history of waters associated with the formation, using long-lived cosmogenic and stable isotope systems. Ratios of ¹²⁹I/I and stable isotope values (δD and δ¹⁸O) were determined in waters from close to 100 wells, ³⁶Cl/Cl ratios for a subset of these samples. A significant group of samples has ¹²⁹I/I ratios between 100 × 10⁻¹⁵ and 200 × 10⁻¹⁵, indicating minimum iodine ages close to 60 Ma. If these ages are corrected for the addition of fissiogenic ¹²⁹I, they are compatible with the depositional age of the Fruitland Formation (Late Cretaceous).Several sets of waters are clearly present within the data. A group dominated by infiltration of recent surface waters is restricted to the uplifted basin margins, with a lateral extent of less than 5 km from outcrop, and is characterized by ¹²⁹I/I ratios in excess of 1500 × 10⁻¹⁵ and meteoric δD, δ¹⁸O, and ³⁶Cl/Cl signatures. The rest of the basin is characterized by several subsets of formation waters which have undergone variable degrees of iodine enrichment through diagenesis as well as variable degrees of dilution. The first subgroup is found in coals of relatively low vitrinite reflectance and moderate enrichment of iodine. This subgroup predominantly consists of entrapped pore fluids, although it may also contain waters which infiltrated the coals at the time of the Laramide uplift, between 25 and 30 Ma. A second subgroup consists of formation waters associated with coals of high vitrinite reflectance. Despite subsequent uplift, the high iodine concentrations and low ¹²⁹I/I ratios of this subgroup, as well as a moderate depletion of deuterium relative to ¹⁸O, suggest that these waters were not significantly altered since the time when diagenetic reactions occurred in the deepest portion of the basin. A third subgroup, with higher δD and δ¹⁸O values as well as higher ¹²⁹I/I ratios, extends roughly west to east at the New Mexico-Colorado state line and corresponds to a region of extensive fracturing of the coalbeds. In this case, the higher ¹²⁹I/I ratios are probably due to contributions of fissiogenic ¹²⁹I through fracture flow, perhaps from deeper formation waters. Our results do not support models of subsequent basin-wide groundwater migration in the Fruitland Formation. The combined use of ¹²⁹I and ³⁶Cl with stable isotope studies provides valuable information as to the hydrologic history of coalbed methane deposits, as well as their potential for commercial exploitation.     

吉林省伊通地区橄榄岩包体的同位素特征与岩石圈地幔时代

吉林省伊通新生代火山群中大孤山所伴生的东小山火山含有丰富的地幔橄榄岩包体,详细的岩石学和矿物学工作显示,这些包体的主要岩石类型为尖晶石二辉橄榄岩,含有少量的方辉橄榄岩和异剥橄榄岩。包体的结构类型多样,包括粒状变晶结构、碎斑状结构、糜棱结构和筛状变晶结构。主量元素及矿物化学资料表明,这些地幔橄榄岩包体大都比较饱满,说明其所经历的部分熔融程度较低。微量元素显示,包体在形成以后经受过不同程度地幔交代作用的影响。矿物平衡温度计算结果表明包体的平衡温度为989～1142℃,来源深度约为40～70km。Sr-Nd-Hf同位素资料反映二辉橄榄岩包体具有亏损地幔的特征。Re-Os同位素资料显示上述岩石圈地幔的主体形成于显生宙期间,少量具有中元古代Re亏损年龄的样品所代表的古老地幔与本区上覆地壳成因无关,可能是软流圈中固有的较古老的大陆岩石圈地幔。     

龙镇地区花岗岩锆石U-Pb年龄和Hf同位素及地质意义

龙镇地区花岗岩位于大、小兴安岭的结合部,属于兴安地块与松嫩地块中的A-I型花岗岩带;该区各岩体岩石类型基本相同,主要为花岗闪长岩和二长花岗岩,地球化学特征显示为高钾钙碱性系列的I型花岗岩。花岗岩中锆石的LA-ICP-MSU-Pb年代学分析结果表明,正达山岩体形成于320～315Ma,模拉布山岩体形成于169±3Ma,朝阳林场岩体形成于187～171Ma。这些花岗质岩浆的就位分别与古生代时期古亚洲洋闭合过程中的块体拼合作用及中生代古太平洋的构造演化有关。Hf同位素成分特征表明,两期花岗岩的源岩均为新元古代-显生宙期间亏损地幔来源的火成岩。结合已发表的Sr-Nd-Hf同位素资料,本文认为兴安地块大陆地壳增生的时间主要为新元古代-显生宙,这与松嫩地块一致,而明显晚于额尔古纳地块的地壳增生时间(中-新元古代),从而揭示了它们不同的地壳演化历史。     

Seasonal variation of gold and arsenic in biogeochemical samples from a disseminated gold deposit in the Northern Cordillera

An orientation survey was conducted over the Quartz Mountain, Oregon, hot-spring type disseminated gold deposit to address three questions critical to successful exploration of the area: What is the relationship between bedrock geology and the trace-element content of trees and soils; do these relationships change seasonally; are these relationships similar in the two tree species which discontinuously blanket the area?Twig, needle and wood samples were collected four times during the year from both ponderosa pine (Pinus ponderosa) and white fir (Abies concolor). Soils were collected once. All samples were analyzed for Au and As and the wood samples were analyzed also for Sb.Arsenic was the best pathfinder element, having little analytical, spatial, or seasonal variation in the twig and needle samples. Anomalous levels were 150 μg/g (ppm) As in pine and 30 μg/g in fir. Gold showed analytical variation of 20–30%, sample duplicate variation up to 90%, spatial changes, and seasonal variation ranging from winter-summer background [10–20 ng/g (ppb) Au] to anomalies of 300–400 ng/g (ppb) Au in pine and 100 μg/g (ppb) Au in fir in the spring and fall. Antimony could not be completely evaluated as a pathfinder element because it was only determined in wood samples.Needles and twigs from both species proved to be viable sample media for exploration of the area. Wood was not a suitable medium because of low, erratic values, perhaps due in part to analytical technique. Needles had 2 to 20 times higher As concentrations than did twigs. Twigs had a slightly higher Au content [25 ng/g (ppb)] than did needles. The pine samples were higher in both elements than were the fir samples. The data, normalized by species, could be treated as one homogeneous data base.The soil Au and As data outlined the mineralization clearly with a central Au anomaly [100 ng/g (ppb) and greater] surrounded by As anomalies [100 μg/g (ppm) and greater] over a distance of 594 m. Neither spring nor fall tree Au anomalies were coincident with the soil Au anomaly. Consistent throughout the year, tree As anomalies coincided with the soil As anomalies, but covered a smaller area. Both the Au and As anomalies in trees appeared to be related to bedrock contact zones rather than to the soil the trees were growing in.