Rune B. Larsen

In situ analysis of trace elements in quartz by using laser ablation inductively coupled plasma mass spectrometry

There are several benefits which would result from the development of an in situ analytical technique for ultra trace elemental analysis of quartz, including rapid screening of possible high-purity quartz resources, by eliminating the need to remove solid and liquid inclusions by expensive dressing techniques prior to chemical analysis of structural impurities. Information on the petrogenetic history of the quartz can also be obtained from the distribution of trace elements. The main purpose of this paper is to describe an analytical method for estimating the concentrations of structural bounded trace elements in quartz. Ž A double focusing sector field inductively coupled plasma mass spectrometry ICP-MS, Finnigan MAT model . ELEMENT , with the CD-1 Guard Electrode and a 266-nm UV laser ablation system was used in the development of the method for in situ analysis of quartz. The following elements are included in the analytical protocol: Al, Ba, Be, Cr, Fe, Ge, K, Li, Mg, Mn, Pb, Rb, Sr, Th, Ž . Ž Ti, U. Analyses were carried out in low mass resolution mrDms300 , except for Mg, Ti, Cr, Fe medium mass . Ž . 29 resolution, MR,mrDmf3500 and K high mass resolution, HR, mrDm)8000 . The isotope Si was used as an internal standard at low resolution, and Si at medium and high resolution. External calibration was done by using the international reference materials: NIST 612, NIST 614, NIST 616, NIST 1830 from the National Institute of Standards and Technology Ž . Ž . NIST , BCS 313r1 from the Bureau of Analysed Samples BAS , the rhyolite RGM-1 reference sample from the United Ž . States Geological Survey USGS , Reston and the certified reference material Apu e Substance No. 1 B silicon dioxide SiO2 Ž . from the Federal Institute for Material Research and Testing, Berlin, Germany BAM . Because of the absence of an SiO 2 blank, the BAM no. 1 SiO was used for the estimation of detection limits. Detection limits for most of the elements are 2 between 0.2 and 0.01 mg g. Analysis time and laser spot size were adjusted so that the raster did not exceed 300 =30 Ž . mm on a 200mm-thick section. New data for the international reference materials BCS 313 r1 BAS and NIST 1830 and the standards BR-K1 and BR-FR2 are reported. To improve the lower limit of quantification and analytical uncertainty at low concentrations, it is important to have calibration curves with well defined intercepts. This can be achieved by the use of certified standards, with trace element concentrations lower than the BAM no.1 SiO or a sample blank. q2002 Elsevier 2 Science B.V. All rights reserved.

Methane-bearing, aqueous, saline solutions in the Skaergaard intrusion, east Greenland

Solutions of H2O−NaCl−CH4 occur in fluid inclusions enclosed by quartz, apatite and feldspar from gabbroic pegmatitites, anorthositic structures and intercumulus minerals within the Skaergaard intrusion. The majority of the fluid inclusions resemble 10 μm diameter sub-to euhedral negative crystals. A vapour phase and a liquid phase are visible at room temperature, solids are normally absent. The salinity of the fluids ranges from 17.5 to 22.8 wt.% NaCl. CH4, which comprises less than six mole percent of the solution, was detected in the vapour phase of the fluid inclusions with Raman microprobe analysis. Homogenization of the fluid inclusions occurred in the liquid phase in the majority of the fluid inclusions, though 10% of the inclusions homogenized in the gas phase. Thermodynamic consideration of the stability of feldspars + quartz, and the C−O−H system, indicates that the solutions were trapped at temperatures between 655 and 770°C, at oxygen fugacities between 1.5 and 2.0 log units below the QFM oxygen buffer. Textural evidence and the composition of the solutions suggest that the fluids coexisted with late-magmatic intercumulus melts and the melts which formed gabbroic pegmatites. These solutions are thought to have contributed to late-magmatic metasomatism of the primocryst assemblages of the Skaergaard intrusion.

Trace element chemistry and textures of quartz during the magmatic hydrothermal transition of Oslo Rift granites

Abstract This study documents the textures and chemical evolution of igneous quartz (Qz) in granite from the Oslo Rift (Norway) during the magmatic-hydrothermal transition. Contrary to the other major igneous phases, primary quartz is well preserved. SEM-CL imaging documents four types of quartz (Qz1-Qz4). Qz1: bright primary magmatic quartz that grew under H2O-undersaturated conditions and developed a conspicuous sector zoning. Qz2: light grey luminescent secondary quartz that surrounds Qz1 and altered Qz1 in a ‘non-destructive’ process. Qz3: is usually darker than Qz2 and intersects Qz1 and Qz2. It is formed by dissolution/recrystallization processes involving saline deuteric fluids. Qz4: found in narrow cracks and patches of black quartz intersecting all the other types. EPMA in situ analyses of the different quartz generations confirm that the intensity of luminescence of quartz is positively correlated with the Ti content of the quartz. Aluminium and K are mostly incorporated in quartz in the form of [AlO4/K+]0 centre defects. In the Drammen granite, the Ti and Al contents of Qz1 averages 200 ppm and 80 ppm respectively. Titanium in Qz1 varies from 50 to 95 ppm in the peralkaline granite known as ekerite, whereas Al is irregular and ranges between 100 ppm and values below the limit of detection (LODAl at 2σ = 14 ppm). In all samples, Qz2 and Qz3 are strongly depleted in Ti and Al compared to Qz1. Either the Ti content in Qz2 is falling gradually towards Qz1 or more abruptly, whereas it is sharp from Qz3 towards Qz1 and Qz2. Potassium is variable in all four quartz types and samples, and ranges from values below the detection limit (LODK, at 2σ = 8 ppm) to 120 ppm. Grains in Qz4, being only 1-2μm wide, could not be resolved with the EPMA beam. In all granites, quartz crystallized from haplogranitic melts at P ~1.5 kbar and T = 700-750°C. SEM-CL and EPMA studies of igneous Oslo Rift quartz illustrate vividly the complex chemical and physical processes that characterize the magmatic-hydrothermal transition in shallow granitic systems and show that the chemistry of primary aqueous fluids is strongly modified from its primary igneous composition before eventually being expelled from the granitic system and perhaps incorporated in ore-forming hydrothermal convection systems.

Late-magmatic immiscibility during batholith formation: assessment of B isotopes and trace elements in tourmaline from the Land’s End granite, SW England

Quartz–tourmaline orbicules are unevenly distributed in the roof segment of the Lands End granite, SW England. This study shows that the orbicules formed from an immiscible hydrous borosilicate melt produced during the late stages of crystallization, and differentiates tourmaline formed by dominantly magmatic and dominantly hydrothermal processes. Trace elements and boron isotope fractionation can be tracked in tourmaline, and create a timeline for crystallization. Tourmaline from the granite matrix has higher V, Cr and Mg content and is isotopically heavier than the later crystallizing inner orbicule tourmaline. Overgrowths of blue tourmaline, occurring together with quartz showing hydrothermal cathodoluminescence textures, crystallized from an aqueous fluid during the very last crystallization, and are significantly higher in Sr and Sn, and isotopically heavier. Tourmaline associated with Sn mineralization is also high in Sr and Sn, but has boron isotopic compositions close to that of the magmatic tourmaline, and is not formed by the same fluids responsible for the blue overgrowths. The ore-forming fluids precipitating tourmaline and cassiterite are likely derived from the same magma source as the granite, but exsolved deeper in the magma chamber, and at a later stage than orbicule formation. Tourmaline from massive quartz–tourmaline rocks is concentrically zoned, with major and trace element compositions indicating crystallization from a similar melt as for the orbicules, but shows a more evolved signature.