Introduction Put simply, the dissolving edges of salt stems, beds and allochthons create temperature, salinity and fracture discontinuities that induce local thermohaline fluid flow. As long as sediments adjacent to a subsiding/ flowing stratiform salt bed or allochthon can maintain some degree of permeability in the salt edge, much of the more interesting subsurface hydrology and reaction interfaces occur in and around brine haloes, centred about intervals or masses of slowly dissolving salt. Ongoing thermohaline-driven dissolution, alteration and flow near the edge of the bed or stem, and ex ..read more

In this second article on "salt edges", we'll look at edge-rock textures and geometries and how various brine interfaces supply brines that are drivers of a range of diagenetic alterations. The first article focused on how caprocks evolve (a sub-set of salt edge rocks)  at the mesoscale. Caprocks not only cap the crest of a salt mass but are also found on the sides (lateral caprocks) and the underbelly of a dissolving salt mass. The third article will focus on the economic significance of fluids and fractures generated in the caprock and edge-rock realms. What happens at sa ..read more

Caprock defined Jackson and Hudec 2017 define caprock as: " a dissolution residue composed predominantly of anhydrite, gypsum, or calcite above a salt body. Caprock forms at the crest of a diapir as halite dissolves, and the residue is chemically altered. Caprock can contain economic minerals, especially sulphur and base-metal sulphides." Keywords in their definition are "above" and "crest of a diaper" Most of us working with evaporites are familiar with the process of cap-rock formation atop the crest of a diapir but may not be familiar with the notion of accumulating caprock-like fractionate ..read more

Evaporites undergoing metamorphism release large volumes of volatile-rich fluids, which are typically saline chloride solutions with elevated levels of sodium and magnesium, as well as chromatophore metals that may colour gemstones growing in ductile meta-evaporitic hosts (Warren, 2016; Chapter 14). Many of these fluids can mobilise and flush metals from adjacent strata, including metalliferous metabasites. Thus, meta-evaporites or their residues often comprise a metallisation series in a metamorphic terrane of a meta-igneous terrane hosting IOCG deposits. Saline sedimentary indications in IOC ..read more

A salty connection? - cooking with salt This second article of three focuses on orthomagmatic-massive evaporite iron-oxide interactions, while the third documents paramagmatic interactions tied to most IOCG sensu-stricto. In both articles, I emphasise aspects of various iron-oxide deposits where evaporites or evaporite-derived hypersaline basinal fluids play a significant role as metal carriers (Fe or Cu or Au) and leave behind textural and mineralogical indications of former massive evaporites (Figure 1). In this article, we look at deposits where dissolving megahalite intervals facilitate fo ..read more

Is there an evaporite connection? Iron-oxide-copper-gold (IOCG) deposits are accumulations that many in the economic geology community would argue have little or no relationship to evaporites. I disagree. So, in this and the next two Salty Matters articles, I question that premise by looking specifically at some of the textures and metasedimentary associations that typify several iron-oxide deposits in both orthomagmatic and paramagmatic settings.  Orthomagmatic deposits discussed in this series of articles are salt-assimilative and mostly internal, if peripheral, to the magma mass or dyk ..read more

Present as the key to the past: Ancient evaporites, the big picture This simple uniformitarian tenet is one of the main underpinnings of Earth Science. Our scientific crystal ball exemplifies the utility of studying present-day saline depositional systems and applying that understanding to ancient evaporites. It allows us to interpret salty textures as; sabkha or subaqueous, deep or shallow, primary or secondary, seepage versus flood hydrology and many other aspects involved in interpreting textures and stacking trends preserved in ancient salty deposits. But there are glaring differences in t ..read more

Introduction Large volumes of ancient saline dolomites not only precipitate as eogenetic brine reflux dolomites, but can also form in the relatively warm burial environments characterising the mesogenetic realm, especially regions of saline basinal waters, in the fault-fed areas often tied to dissolving evaporites. In this context, saddle dolomite is an archetypal burial carbonate precipitated from hot salty basinal fluids (Figure 1). Some saddle dolomite precipitates are intimately associated with a range of indicators of thermally altered evaporite salts, especially burial anhydrite spar; ot ..read more

Stated simply; the dolomite problem encapsulates the notion that there are no viable modern analogs for ancient massive platform-scale dolomites. This is a scaling quandary that has puzzled geoscientists for more than two centuries. Modern dolomite is either a primary muddy precipitate or a penecontemporaneous finer-grained replacement across a number of Holocene depositional settings. Settings that are mostly hypersaline, schizohaline, periodically or permanently low in oxygen, and frequently associated with a rich microbial population dominated by sulphate reducers and/or methanogens. These ..read more

Hydrogen, the most abundant element in the Universe, was recognised in 1776 by Henry Cavendish, and its name was coined in 1783 by Antoine Lavoisier. Hydrogen is considered a future green energy carrier, which can be utilised in the energy, transport, and chemical sectors. Hydrogen-based energy technologies are a promising solution to fulfil the future zero-emission scenario and perhaps ensure the energy independence of many countries.  However, in its natural state, hydrogen is reactive and mobile, so identifying natural regions of enrichment and designing large-scale, efficient and safe ..read more