Abstract:The Kara ore node is located within the Sretensk-Kara ore region of East Transbaikalia. The geological structure of this area is complex due to its location within the Mongol-Okhotsk suture, the zone wherein the Siberian and Mongolia-China continents collided into each other at the turn of the Early and Middle Jurassic. During the plate collision, intense magmatism was accompanied by the formation of focal-dome, dome-ring and other structures. The Kara ore node is controlled by the Ust-Kara focal dome-ring structure. The central part of latter is composed of KaraChacha granitoids from the Amudzhikan-Sretensk intrusive complex (J3-K1) with the system of subvolcanic and vein formations, including grorudites. It is suggested that gold mineralization in the study area is genetically related to grorudites; however, physical and chemical conditions for the formation of these alkaline rocks, their genesis and role in the hydrothermal gold-ore process still have not been sufficiently investigated. To this end, the authors of this paper have studied fluid inclusions (FI) in quartz from these rocks. It has been found that quartz porphyry phenocrysts in grorudite contain FI of diverse forms, the size of which ranges from 5 to 48 microns. Measured temperatures of ice melting (-2.5°C) and complete homogenization into liquid (350 °C) show that the concentration of salts in the fluid amounts to 4.2 wt % of eq. NaC, its density is 0.64 g/cm 3 , and the pressure is 1.6 kb. At LA-ICP-MS of individual FI, clear analytical signals were derived from Na and K. As, Mo, Sb, Cs, W, and Hg were traced in significant quantities. The Raman scanning showed the presence of N2 in the primary (substantially gaseous) FI, and CO2, N2, and CH4 in the primary-secondary FI.

The most voluminous silicic volcanic eruptions in the geological past were associated with caldera collapses above giant silicic magma reservoirs. The thermal evolution of these subcaldera magma reservoirs controls the volume of eruptible magma and eruptive style. Here we combine high-precision zircon U-Pb geochronology, trace element analyses of the same mineral grains, and mass balance modeling of zircon trace element compositions allowing us to track the thermal and chemical evolution of the Oligocene Fish Canyon Tuff magma reservoir (Colorado, United States) as a function of absolute time. Systematic compositional variations in U-Pb dated zircons record ~440 k.y. of magma evolution. An early phase of volumetric growth was followed by a period of cooling and crystallization, during which the Fish Canyon magma approached complete solidifi cation. Subsequent remelting, due to underplated andesitic recharge magmas, began 219 ± 45 k.y. prior to eruption, and led to the generation of ~5000 km3 of eruptible crystal-rich (~45 vol%) dacite. Age-equivalent, but compositionally different, zircons in an andesite enclave from late-erupted Fish Canyon Tuff tie the growth and thermal evolution of the upper-crustal reservoir to a lower-crustal magma processing zone. Our results demonstrate that the combination of high-precision dating and trace element analyses of accessory zircons can reveal invaluable information about the chemical and thermal histories of silicic magmatic systems and provides critical input parameters for fl uid dynamic modeling

Utilization of metallic engineered nanoparticles (ENP) is progressing rapidly; therefore, characterization of their most important properties, e.g., size/mass, elemental composition, and number concentration, is inevitable and currently uses a set of different techniques. In this work, a new setup is proposed for the quantitative size and mass determination of ENPs employing a monodisperse microdroplet generator (MDG) with transport efficiencies >95% coupled to an ICPMS. Two different MDG sample introduction configurations (vertical and horizontal) were tested, and their performance characteristics were evaluated. Due to a 5-fold reduced temporal jitter resulting in a shorter measurement time, the horizontal droplet introduction approach was used for the analysis of ENPs. With this setup, the quantification of Au, Ag, and CeO2 nanoparticles of different sizes and polydispersities was achieved. Results are compared to complementary techniques such as transmission electron microscopy (TEM) and asymmetric flow field flow fractionation (AF4), and advantages as well as limitations of this newly proposed technique are discussed.

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Flame spray synthesis was used to produce a reference nano-material with a customized composition for use in LA-ICP-MS.