The origin of celestine–quartz–calcite geodes associated with a basaltic dyke, Makhtesh Ramon, Israel

Abstract

Spectacular celestine geodes occur in a Jurassic peri-evaporitic sequence (Ardon Formation) exposed in Makhtesh Ramon, southern Israel. The geodes are found only in one specific location: adjacent to an intrusive contact with a Lower Cretaceous basaltic dyke. Celestine, well known in sedimentary associations worldwide and considered as a low temperature mineral, may therefore be associated with magmatic-induced hydrothermal activity. Abundant fluid inclusions in celestine provide valuable information on its origin: gas-rich inclusions in celestine interiors homogenized at T≥200°C whereas smaller liquid-rich inclusions record the growth of celestine rims at T≤200°C. Near 0°C melting temperatures of some fluid inclusions and the occurrence of hydrous Ca-sulphate solid crystals in other inclusions indicate that celestine precipitated from variably concentrated Ca-sulphate aqueous solutions of meteoric origin. Celestine crystallized from meteoric water heated by the cooling basaltic dyke at shallow levels (c. 160 m) during a Lower Cretaceous thermal perturbation recorded by regional uplift and magmatism. The 87Sr/86Sr ratio of geode celestine, 0.7074, is similar to that measured in the dolostones of the host Jurassic sequence, but differs markedly from the non-radiogenic ratio of the dyke. Strontium in celestine was derived from dolostones preserving the 87Sr/86Sr of Lower Jurassic seawater, while sulphur (δ34S = 19.9‰) was provided by in situ dissolution of precursor marine gypsum (δ34S = 16.8‰) indicated by relict anhydrite inclusions in celestine. Low-temperature meteoric fluid flow during the Campanian caused alteration of the dyke into secondary clays and alteration of geodal celestine into quartz, calcite and iron oxides.

Characterisation, axial anisotropy, and formation conditions of celestine minerals from the Jabal Eghei (Nuqay) late Neogene – Pleistocene volcanic province, southeastern edge of the Sirt Basin, southern Libya: Constraints on the mineralogical geothermometer

“…The celestines investigated were most probably formed as a secondary mineral, repositioned into the gypsum and/or anhydrite layer, at temperatures over ∼373 K (∼100°C) and pressures over 250 bars. The subsequent formation of geodes or druses and nodules is further attributed to the clustering of celestine across sedimentary formations, but under surface conditions (similar to Anenburg et al, 2014). The constraints on the differently inserted Pb 2+ , Ba 2+ and Ca 2+ cations into the structure are characterised as a secondary factor for the unit-cell parameters expansion, including the observed slight c 0 < b 0 < a 0 axial anisotropy variations.…”

“…Few publications exist focusing on the origin of the North African (e.g. Anenburg et al, 2014) and in particular central-southern Libyan basalts and associated celestine occurrences (e.g. Elshaafi and Gudmundsson, 2017;Radivojević et al, 2015;Cvetković et al, 2022); hence our interpretation of the Jabal Eghei celestine provides new insight into the axial anisotropy of the celestine crystals investigated and their growth.…”

“…Celestine as a low-temperature mineral has frequently been associated with magmatic-hydrothermal activity at temperatures S16 and S17): below 300°C (Anenburg et al, 2014). To reconstruct minerogenesis, we take into consideration celestine formation conditions, in particular, the typifying shallow crustal marine, evaporitic palaeoredox environments (Hanor 2000(Hanor , 2004.…”

“…The subsequent process of precipitation and formation of celestine-bearing druses or nodules (e.g. Anenburg et al, 2014) was probably initiated once the ) stand for all 1 to 5 investigated samples (green tick marks), having the same ambient pressure (Table 8). The sketch shows three scenarios: temperature remains constant by the pressure increase (orange interrupted lines); temperature increases by the pressure increase (yellow full lines with approximate slope); and temperature increases by the pressure decrease (pink dotted lines with approximate slope).…”

“…In addition, celestine occurrences can be as hydrothermal veins associated with mafic volcanism (e.g. Baskina et al , 1978; Brigatti et al , 1997; Radivojević et al , 2015; Garcia et al , 2016; Tortelli et al , 2022) or basaltic dykes (Anenburg et al , 2014). Occurrences of younger Quaternary celestines comparable to those investigated in southern Libya have been recorded only rarely (e.g.…”