Iron mineralization and dolomitization in the Paran Fault zone, Israel: implications for low‐temperature basinal fluid processes near the Dead Sea Transform

Abstract

Petrography, Eh-pH calculations and the stable isotope composition of oxygen are used to interpret geochemical processes that occurred during iron oxide mineralization and dolomitization along the Menuha Ridge segment of the Paran Fault, southern Israel, adjacent to the Dead Sea Transform (DST). Iron mineralization is strongly localized in the fault zone as ferruginous lenses, whereas Fe dolomitization spreads laterally into the CenomanianTuronian carbonate host rock as stratabound beds. The average oxygen isotope fractionation between syngenetic quartz and iron oxides in the ferruginous lenses gives a temperature of 50 ± 10°C and d 18 O SMOW water ¼ )3.5&; consistent with an origin from metalliferous groundwater flow in the sedimentary basin. Ferroan dolomite initially formed under strongly reducing conditions, but this was followed by oxidation and pseudomorphic replacement of the dolomite by a mesh of fine-grained iron oxides (simple zoned dolomites). This cycle of ferroan dolomite formation and replacement by iron oxides was repeated in complex zoned dolomites. Dolomite oxygen isotope compositions fall into two groups: a high d 18 O group corresponding to the simple zoned dolomites and non-ferroan dolomites and a low d 18 O group corresponding to the complex zoned dolomites. Waterrock calculations suggest that the epignetic dolomites formed under fluid-buffered conditions: the high d 18 O group are indicated to have formed at temperatures of ca. 25°C for waters with d 18 O ¼ )4 to 0&; the low d 18 O complex zoned dolomites at 50-75°C for waters with the same isotopic composition. A kinetic calculation for a complex zoned dolomite-bearing bed indicates that dolomitization must have occurred at high values of the dolomite saturation index. This requirement for high Mg supersaturation and the indication that epigenetic dolomitization is more protracted in stratigraphically deeper formations located closer to the DST is consistent with models proposing that Mg-rich solutions originated in the Dead Sea Rift.

Influence of climate and dolomite composition on dedolomitization: insights from a multi-proxy study in the central Oman Mountains

“…However, oxidation of ferroan dolomite is not necessarily accompanied by calcitization of dolomite. Subaerial exposure can convert ferroan dolomite into iron oxide grains or aggregates by oxidation and pseudomorphic replacement (Zeidan and Basyuni 1998;Grosz et al 2006). The fact that goethite is formed rather than hematite (no relicts or pseudomorphs of hematite are present) is also consistent with conditions of low temperature and pH found at surface conditions, high water activity [H 2 O], and low iron supply rates (Yapp 2001).…”

Tracing end-member fluid sources in sub-surface iron mineralization and dolomitization along a proximal fault to the dead sea transform

“…Regional-scale faulting (the Negev Shear zone) related to the Dead Sea Transform, which initiated in the Miocene, facilitated the rise of the over pressured solutions along fault lines and allowed the dolomitization and mineralization of the overlying carbonate rocks (Bartov, 1974;Ilani et al, 1988). The sedimentary basinal setting of the mineralization was confirmed by oxygen isotope studies of ferruginous lenses, which showed that they formed at temperatures of 50 ± 10°C (Grosz et al, 2006).…”

“…The dolomite is characterized by a deep-red colouration, which frequently stands out against the pale-coloured limestone; consequently beds can be traced easily along strike (Grosz et al, 2006). Dolomitization at Zvar Habaqbuq (ZH) in the west of the area occurs in the Ora and Gerofit formations exposed on the south side of the Paran fault (Figs.…”

“…This dolomite can be followed approximately 1000 m from the fault where it terminates and gives way to unaltered biomicritic limestone. Grosz et al (2006) showed that the dolomites can be classified into three textural and mineralogical types.…”

“…Geochemical studies of groundwater wells and theoretical calculations have both suggested that density driven migration of saline Mg-rich brines from the Dead Sea Rift into adjacent carbonate rocks could have resulted in dolomitization (Starinsky, 1974;Stanislavsky and Gvirtzman, 1999). The need to examine this alternative is reinforced by detailed petrographic and oxygen isotope studies of dolomites (Grosz et al, 2006, see next section), which suggest that at least two fluid flow patterns are involved in the dolomitization: an earlier one characterized by T 6 50°C and a later one characterized by T P 50°C and lower d 18 O groundwater. Pb and Sr isotopes are ideal tools for elucidating the origin of the fluids involved in the iron mineralization and dolomitization, since they monitor elements such as Fe and Mg, respectively.…”