Styles of Alteration of Ti Oxides of the Kimberlite Groundmass: Implications on the Petrogenesis and Classification of Kimberlites and Similar Rocks

Abstract

The sequence of replacement in groundmass perovskite and spinel from SK-1 and SK-2 kimberlites (Eastern Dharwar craton, India) has been established. Two types of perovskite occur in the studied Indian kimberlites. Type 1 perovskite is found in the groundmass, crystallized directly from the kimberlite magma, it is light rare-earth elements (LREE)-rich and Fe-poor and its ∆NNO calculated value is from −3.82 to −0.73. The second generation of perovskite (type 2 perovskite) is found replacing groundmass atoll spinel, it was formed from hydrothermal fluids, it is LREE-free and Fe-rich and has very high ∆NNO value (from 1.03 to 10.52). Type 1 groundmass perovskite may be either replaced by anatase or kassite along with aeschynite-(Ce). These differences in the alteration are related to different f (CO 2) and f (H 2 O) conditions. Furthermore, primary perovskite may be strongly altered to secondary minerals, resulting in redistribution of rare-earth elements (REE) and, potentially, U, Pb and Th. Therefore, accurate petrographic and chemical analyses are necessary in order to demonstrate that perovskite is magmatic before proceeding to sort geochronological data by using perovskite. Ti-rich hydrogarnets (12.9 wt %-26.3 wt % TiO 2) were produced during spinel replacement by late hydrothermal processes. Therefore, attention must be paid to the position of Ca-Ti-garnets in the mineral sequence and their water content before using them to classify the rock based on their occurrence.

Perovskite geochronology and petrogenesis of the Neoproterozoic Mad Gap Yards ultramafic lamprophyre dykes, East Kimberley region, Western Australia

“…The Ti-rich 579 hydroandradite in the Mad Gap Yards lamprophyre is interpreted to be secondary in origin, 580 formed from the replacement of magnetite, and therefore not relevant to rock classification 581 (cf. Xu et al 2018). 582 20 Spinel compositions follow trend 2 shown by UMLs worldwidea compositional 583 trend that was probably controlled by the high phlogopite content of the dykes (Fig.…”

Magma Mingling in Kimberlites: Evidence from the Groundmass Cocrystallization of Two Spinel-Group Minerals

“…These rocks clearly present a petrographic challenge due to the hybrid nature and common strong overprint by late hydrothermal and supergene processes. Such alteration processes lead to the crystallization of abundant secondary minerals and to the modification of the original bulk composition, making the study of the early magmatic processes difficult [2,3]. The study of rare fresh kimberlite samples…”

Role of trace element Pedogeochemistry in Diamond Exploration- A first Report from Lattavaram Kimberlite Cluster, Wajrakarur Field, Eastern Dharwar Craton, southern India

“…In India, majority of the documented research work related to kimberlites provided a great knowledge in understanding the petrology, geochemistry, geochrnology and geophysics of Indian kimberlites (e.g. Akella et al, 1979;Reddy 1987, Rao et al, 1998Anil Kumar et al, 2002;Chalapathi Rao et al, 2005;Paul et al, 2006;Anil Kumar et al, 2007;Chalapathi Rao et al, 2009;Ian et al, 2011;Chalapathi Rao et al, 2016;Dongre et al, 2016;Xu et al, 2017;Shaikh et al, 2018). Despite the vast research on petrological aspects of kimberlites and lamproites, published literature pertaining to application of soil or regolith geochemistry in identifying mineral deposits in general and diamond exploration in particular, in the Indian context, is limited to a very few publications (e.g.…”