scholarly journals Mineralogy and Geochemistry of Sr-Bearing Phosphates from the Nanping No. 31 Pegmatite (SE China): Implications for Sr Circulation and Post-Magmatic Processes in Granitic Systems

Minerals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 541
Author(s):  
Can Rao ◽  
Ru-Cheng Wang ◽  
Frédéric Hatert ◽  
Run-Qiu Wu ◽  
Qi Wang
Keyword(s):  
Chemical Composition ◽  
Low Temperatures ◽  
Hydrothermal Fluids ◽  
Sr Isotopes ◽  
Sr Isotope ◽  
Southeastern China ◽  
Direct Precipitation ◽  
Magmatic Processes ◽  
Se China

Although Rb/Sr ratio and Sr isotopes are routinely modeled to determine petrogenetic processes and sources for granitic systems, the post-magmatic path and crystallization of Sr in granitic systems have not been thoroughly elucidated to date. In this study, we present the petrography, chemical composition and isotopic 87Sr/86 of Sr-bearing phosphates from the Nanping No. 31 pegmatite in Southeastern China, helping to characterize post-magmatic stages and geochemical recirculation of Sr in granitic systems. K-feldspar and primary apatites occur as major “primary Sr minerals”, the occurrences of secondary Sr phosphates (strontiohurlbutite, palermoite and goyazite) and Sr-rich phosphates (apatites, hurlbutite, bertossaite and fluorarrojadite-(BaNa)) reflect the transport, concentration and recrystallization of Sr in granitic systems. The mobilization and recrystallization of Sr in granitic systems are mainly controlled by the variation in alkalinity of hydrothermal fluids. Two post-magmatic recirculations of Sr are proposed in the Nanping No. 31 pegmatite: (1) breakdown of the “primary Sr mineral” (K-feldspar and primary apatites) and crystallization of secondary Sr-bearing phases; and (2) replacement of secondary Sr-bearing phosphates and direct precipitation of later palermoite and goyazite from later Sr-rich fluids at low temperatures. The Sr isotope features of Sr-bearing phosphates suggest that the emplacement and consolidation processes of the Nanping pegmatite involved the participation of externally derived fluids.

Hydrothermal Sr contamination of the Dippin sill, Isle of Arran, Western Scotland

1984 ◽  
Vol 48 (348) ◽  
pp. 311-322 ◽  
Author(s):  
A. P. Dickin ◽  
C. M. B. Henderson ◽  
F. G. F. Gibb
Keyword(s):  
Stable Isotope ◽  
Hydrothermal Alteration ◽  
Closed System ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Drill Core ◽  
Sr Isotope ◽  
Core Section ◽  
High Silica ◽  
Isotope Measurements

Abstract The Dippin sill, which is emplaced into the Triassic sediments of SE Arran, is an alkaline basic sheet which displays pronounced hydrothermal alteration. The 40-m-thick sill has suffered pervasive contamination with radiogenic Sr, introduced from the Triassic sediments by hydrothermal fluids. Stable isotope measurements suggest that fluids were of meteoric origin, but were restricted to a small closed-system circulation. Initial 87Sr/86Sr ratios in the sill were raised from an original value of 0.7032 to a maximum of 0.7091, contamination being especially pronounced near the contacts at Dippin Head itself (localities 12 and 14) and in a drill core section through the sill above Dippin. Hydrothermal Sr was incorporated into an early-formed high-CaO, high-Sr analcime, which replaced unstable high-silica nepheline in interstitial patches. However, this high-CaO analcime, along with plagioclase, was later replaced by a low-CaO, low-Sr analcime, allowing Sr leaching from the margins of the sill. Hydrothermal fluids are thought to have migrated up to 1 km laterally, up the dip of the sill, mainly via tension joints forming in the cooling intrusion. Pooling of hot fluids at the upper end of the sill probably raised water/rock ratios in this region and allowed greater Sr contamination during mineralogical alteration. The undersaturated mineralogy of the sill accounts for its pervasive hydrothermal Sr contamination, which contrasts markedly with the relatively undisturbed Sr isotope compositions of Hebridean granites involved in hydrothermal systems.

scholarly journals Orange opals from Buriti dos Montes, Piauí: solid inclusions as genetic guides

2015 ◽  
Vol 68 (1) ◽  
pp. 53-59 ◽  
Author(s):  
Gisele Tavares Marques ◽  
Marcondes Lima da Costa ◽  
Érico Rodrigues Gomes
Keyword(s):  
Chemical Composition ◽  
Aqueous Solutions ◽  
High Stability ◽  
Hydrothermal Fluids ◽  
Northeastern Brazil ◽  
Quartz Crystals ◽  
Hydrothermal Processes ◽  
Hydrothermal Environment

Orange opals from Buriti dos Montes (Piauí, northeastern Brazil) have gemological properties that favor their use as jewelry; these characteristics include their colors, transparency, relatively high stability and hardness. The exotic content of solid inclusions provides greater beauty to the opals of this region. These opals originated from hydrothermal processes and are found mainly as veinlets and veins in the sandstones of the Serra Grande Group, sectioned by diabase dikes and sills of the Sardinha Formation. Solid inclusions, such as bubbles, botryoidal aggregates, dendrites, and nodules, among others, consist mainly of kaolinite, hematite/goethite and quartz and influence the chemical composition of opals. Intense zoning of quartz crystals and high values of Ba and Fe suggest that opal deposits were formed in a hydrothermal environment. Diabase dykes could have been responsible for heating the hydrothermal fluids. Sandstones, rich in aqueous solutions, also contributed to the available silica for the saturation of these solutions, and fractures enabled the migration and entrapment of hydrothermal fluids, resulting in the mineralized veins.

Formation and Modification of Oxide Networks by Chemical Polymerization

1983 ◽  
Vol 24 ◽  
Author(s):  
Bulent E. Yoldas
Keyword(s):  
Chemical Composition ◽  
Network Structure ◽  
Material Properties ◽  
Low Temperatures ◽  
Ceramic Materials ◽  
The Other ◽  
Equilibrium Conditions ◽  
Chemical Polymerization ◽  
Structural Modifications ◽  
Structure Synthesis

ABSTRACTThe properties of glass and ceramic materials are largely determined by the types and distribution of bonds in the network structure. Since conventional methods of forming these materials by melting or sintering do not allow significant variations from the equilibrium conditions, the properties of these materials are generally fixed by the chemical composition and crystalline structure. Synthesis of these materials by chemical polymerization at low temperatures, on the other hand, permits significant modifications to the ultrastructure. These structural modifications in turn modify the material properties, without compositional alterations. In this presentation, further studies of structure-modifying parameters are discussed.

scholarly journals Listvenites: new insights of a hydrothermal system fossilized in Cerro Matoso peridotites, Montelíbano, Córdoba Department, Colombia

2020 ◽  
pp. 67-84
Author(s):  
Andrés Castrillón ◽  
Javier Guerrero
Keyword(s):  
Chemical Analysis ◽  
Fracture Zone ◽  
Hydrothermal System ◽  
Low Temperatures ◽  
Mineralogical Composition ◽  
Climatic Conditions ◽  
Hydrothermal Fluids ◽  
Metasomatic Alteration ◽  
Mineralogical Association

The products of metasomatic alteration (e.g., carbonation) of peridotites are called listvenites. Based on a description of the outcrops in the laterite deposit at Cerro Matoso located in the NW of Colombia, the mineralogical composition confirmed by petrography, and a chemical analysis performed with XRF and WDS/EDS, the previous unit called tachylite is redefined as listvenite. Two types of listvenites are described: listvenite A, with the mineralogical association of quartz + siderite + phyllosilicates + goethite +/- magnetite, and listvenite B, with the association of siderite + phyllosilicates + goethite. Cr-spinel relics accompanied by Mn-siderite and neoblastic textures, indicate their origin from peridotites, where Mn-Fe would have been deposited by hydrothermal fluids. Hydrothermal reducing environments with alkaline fluids and low temperatures should have favored the formation of listvenites that are observed along a fracture zone, oriented WNW-ESE at Pit-1 in Cerro Matoso. Due to exposure to climatic conditions since the Eocene, but definitively since the last Andean Orogeny, listvenites were affected, like all the rocks in the Cerro Matoso deposit, by intense supergene weathering and leaching processes, which could make their true origin unclear.

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