Geological & Science reports
Updated Competent Person’s Report on the Shefa Gems® Ltd Gemstone Assets Prepared for Shefa Gems Ltd
Hibonite (CaAl12O19) is a constituent of some refractory calcium-aluminum inclusions (CAIs) in carbonaceous meteorites, commonly accompanied by grossite (CaAl4O7) and spinel. These phases are usually interpreted as having condensed, or crystallized from silicate melts, early in the evolution of the solar nebula. Both Ca-Al oxides are commonly found on Earth, but as products of high-temperature metamorphism of pelitic carbonate rocks.
Although hydrogen is the most abundant element in the solar system, the mechanisms of exchange of this element between the deep interior and surface of Earth are still uncertain. Hydrogen has profound effects on properties and processes on microscopic-to-global scales. Here we report the discovery of the first hydride (VH2) ever reported in nature. This phase has been found in the ejecta of Cretaceous pyroclastic volcanoes on Mt Carmel, N. Israel, which include abundant xenoliths containing highly reduced mineral assemblages…
The new mineral species carmeltazite, ideally ZrAl2Ti4O11, was discovered in pockets of trapped melt interstitial to, or included in, corundum xenocrysts from the Cretaceous Mt Carmel volcanics of northern Israel, associated with corundum, tistarite, anorthite, osbornite, an unnamed REE (Rare Earth Element) phase, in a Ca-Mg-Al-Si-O glass. In reflected light, carmeltazite is weakly to moderately bireflectant and weakly pleochroic from dark brown to dark green. Internal reflections are absent.
The minimum oxygen fugacity (fO2) of Earth’s upper mantle probably is controlled by metal saturation, as defined by the iron-wstite (IW) buffer reaction (FeO >Fe + O). However, the widespread occurrence of moissanite (SiC) in kimberlites, and a suite of superreduced minerals (SiC, alloys, native elements) in peridotites in Tibet and the Polar Urals (Russia), suggest that more reducing conditions (fO2 = 6–8 log units below IW) must occur locally in the mantle. We describe pockets of melt trapped in aggregates of corundum crystals ejected from Cretaceous volcanoes in northern Israel which contain high-temperature mineral assemblages requiring extremely low fO2 (IW < 10). One abundant phase is tistarite (Ti2O3), previously known as a single grain in the Allende carbonaceous chondrite (Mexico) and believed to have formed during the early evolution of the solar nebula. It is associated with other reduced phases usually found in meteorites. The development of super-reducing conditions in Earth’s upper mantle may reflect the introduction of CH4 + H2 fluids from the deep mantle, specifically related to deep-seated volcanic plumbing systems at plate boundaries.
Melts and fluids are magic active components of the solid Earth, which keep the Earth dynamic and evolving. However, our knowledge of such components is deficient, especially under mantle conditions.
Moissanite (SiC) has been found in different mantle and mantle-generated rocks from different tectonic settings, and its formation may be closely related to the mantle melts/fluids. We have investigated SiC from kimberlites, mantle xenoliths, Tibetan ophiolites, and ejecta from volcanoes in Israel.
This paper gives a summary of the genetic model for the Mt. Carmel gem-bearing volcanic system and especially the origins of its remarkable suite of super-reduced (low oxygen fugacity) minerals. It then compares this suite to the super-reduced mineral association that has been found in several ophiolite occurrences, both in Tibet and the Polar Urals, and concludes that these occurrences reflect processes like those that have produced the Carmel Sapphire and other reduced minerals in the Mt Carmel volcanics. It also draws attention to the occurrence of this suite of minerals in explosive volcanoes on the Kamchatka Peninsula (NE Russia) and suggests that these processes may be more widespread than previously realized.
The European Journal of Mineralogy is the combined outlet for several mineralogical and geochemical societies in Europe. It is widely read and cited. Note: This article was named as the Editor’s Choice for 2017 and will be available on Open Access for one year.
