Continental Brines Research Articles

A Group of Papers on Fluid Inclusion Research Applied to Ore Deposits: An Introduction

The group of six papers and one scientific contribution that follow this brief introduction illustrate the application of fluid inclusion research to ore deposits, a field pioneered by Edwin Woods Roedder (July 30, 1919–August 1, 2006) (Fig. 1⇓), who contributed nearly 400 published works during a career that spanned more than three-quarters of a century. His first paper was published in 1935 (Roedder, 1935), on the topic of black sulfur at Hillborn, New York; his final (posthumous) publication in 2008 was as a coauthor on the thermal history of Yucca Mountain, Nevada (Whelan et al., 2008). Many readers of this journal will know that Ed Roedder was the leader in the field of fluid and melt inclusions (Roedder, 1984b), but some may not realize that he also made significant contributions in other areas, including experimental petrology of the K2O-FeO-Al2O3-SiO2 system (Roedder, 1951), the geologic storage of radioactive waste (Roedder, 1957), and lunar petrology (Roedder and Weiblen, 1970). Ed’s most significant contributions were related to the critical role that fluids and related processes play in ore formation; a large number of his publications were related to mineral deposits and ore genesis, with 25 of these published in Economic Geology between 1962 (Roedder, 1962) and 1989 (Anderson et al., 1989). A compilation and summary of much of Ed’s work up until the early 1980s is included in his well-known publication, Fluid Inclusions (Roedder, 1984b). A complete listing of Ed Roedder’s publications is available at the Edwin Woods Roedder Memorial Virtual Library at the following location: . Some lithium salts exhibit high solubilities in aqueous solutions, leading to high concentrations in continental brines, postmagmatic hydrothermal systems, and rare-element pegmatites, despite lithium being a trace element in …

Fluid inclusion analysis of twinned selenite gypsum beds from the Miocene of the Madrid basin (Spain). Implication on dolomite bioformation

This research work is centred on continental lacustrine gypsum deposits of Miocene age cropping out in the easternmost part of the Madrid Basin. These gypsum deposits, accumulated in a continental saline lake, are characterized by a spectacular, distinctive Christmas-tree morphology and a peculiar dolomite replacement. A combination of microscopic (petrography and scanning electron microscopy) and analytical techniques (fluid inclusion microthermometry, X-ray energy dispersive spectroscopy and X-ray diffractometry) was used in order to study the crystallographic distribution and the composition of the fluid inclusions within the gypsum. The objectives were to characterize the continental brine from which the mineral precipitated, and to detect mineral and element traces that could indicate early diagenetic processes altering the gypsum deposits. Data from primary fluid inclusions indicated that gypsum precipitated from an aqueous fluid (lake water) of low to moderate total salinity (between 20 and 90 g/L NaCl). Secondary fluid inclusions represent interstitial lake brine in contact with gypsum, slightly enriched in total salt content as crystal formation proceeded. Textural, ultrastructural and microanalytical analysis indicate that the presence of dolomite precipitates inside the gypsum layers is related to the microbial colonization of the gypsum deposits and the biomineralization of the cell walls and extracellular polymeric substances around the cells. Our investigation emphasizes necessity of a multidisciplinary approach to assess geobiological processes.

Source of solutes to the coastal sabkha of Abu Dhabi

An ascending-brine model is proposed to address the observed isotope geochemistry, solute composition, and solute and water fluxes in the coastal sabkha of the Emirate of Abu Dhabi. Mass-balance measurements document that >95% of the solutes are derived from ascending continental brines; minor amounts are derived from rainfall and from groundwater entering from up- gradient areas. Nearly 100% of the annual water loss is from evaporation and not lateral discharge. Direct rainfall on the sabkha and subsequent recharge to the underlying aquifer account for ∼90% of the annual water input to the system; the remaining 10% comes from both lateral and ascending groundwater flow. Thus, the water and solutes in this system are from different sources. Solute concentrations of conservative (i.e., nonreactive) elements in the coastal, sabkha-covered aquifer are consistent with the fluid pore volumes of ascending brine calculated from hydrologic properties. Calcium to sulfate ratios and sulfur isotopes are consistent with this source of solute from the underlying Tertiary formations. Recharging rainwater dissolves halite and other soluble minerals on the surface, causing the solution to become more dense and sink to the bottom of the aquifer where it vertically mixes with less dense ascending brines. Solutes are returned to the surface by capillary forces and recycled or lost from the system by eolian or fluvial processes. Thus, the system becomes vertically mixed, consistent with the presence of tritium throughout the aquifer; but there is essentially no horizontal mixing of seawater with groundwater. The observed seawater solutes in the supratidal zone come from interstitial seawater trapped by the rapid progradation of the sediments into the Arabian Gulf and are not refluxed or laterally mixed. The ascending- brine model contrasts significantly with both the seawater-flooding and evaporative- pumping models previously proposed as a source of solutes to the coastal sabkha of the Emirate of Abu Dhabi. Use of these earlier models leads to incorrect conclusions and raises serious questions about their applicability in the evaluation of sabkhat in the geologic record.

Redbed‐associated sabkhas and tidal flats at Shark Bay, Western Australia: Their significance for genetic models of stratiform Cu‐(Pb‐Zn) deposits

Interaction of metalliferous continental brines with biogenic sulphide is the basis of some syngenetic and early diagenetic models for the formation of Cu‐(Pb‐Zn) sulphides during a depositional cycle of carbonates in restricted marine environments. A variation of these models (an ‘evaporative concentration‐lateral groundwater flow’ model) is proposed, using hydrological, geochemical and biological data from low metal, but otherwise pertinent redbed‐associated, sabkha, tidal flat and subtidal environments at Nilemah Embayment, in Hamelin Pool (Shark Bay, Western Australia). The model is constrained by: (i) the short time available for ore accumulation during a single depositional cycle; (ii) limitation of adequate rates of bacterial sulphate reduction for the formation of an ore deposit to near‐surface sediments; (iii) restriction of the most favourable ore‐forming sites to the intertidal zone and the littoral shelf; (iv) coincidence in these sites of laterally‐flowing marine/meteoric groundwater brine, a...

Halite saltern in the Canning Basin, Western Australia: a sedimentological analysis of drill core from the Ordovician‐Silurian Mallowa Salt

ABSTRACTThe Late Ordovician‐Early Silurian Mallowa Salt of the Carribuddy Group, Canning Basin, north‐west Australia, is the largest halite deposit known in Australia, attaining thicknesses of 800 m or more within an area of approximately 200 000 km2. Study of 675 m of drill core from BHP‐Utah Minerals’ Brooke No. 1 well in the Willara Sub‐basin indicates that the Mallowa Salt accumulated within a saltern (dominantly subaqueous evaporite water body) that was subject to recurrent freshening, desiccation and exposure. Textures and bromine signatures imply a shallow water to ephemeral hypersaline environment typified by increasing salinity and shallowing into evaporitic mudflat conditions toward the top of halite‐mudstone cycles (Type 2) and the less common dolomite/anhydrite‐halite‐mudstone cycles (Type 1). The borate mineral priceite occurs in the capping mudstones of some cycles, reinforcing the idea of an increasing continental influence toward the top of mudstone‐capped halite cycles.The rock salt in both Type 1 and Type 2 cycles typically comprises a mosaic of large, randomly orientated, interlocking halite crystals that formed during early diagenesis. It only partially preserves a primary sedimentary fabric of vertically elongate crystals, some with remnant aligned chevrons. Intraformational hiati, halite karst tubes and solution pits attest to episodic dissolution. Stacked Type 2 cycles dominate; occasional major recharges of less saline, perhaps marine, waters in the same area produced Type I cycles.The envisaged saltern conditions were comparable in many ways to those prevailing during the deposition of halite cycles of the Permian Salado Formation in New Mexico and the Permian San Andres Formation of the Palo Duro Basin area in Texas. However, in the Canning Basin the cycles are characterized by a much lower proportion of anhydrite, implying perhaps a greater degree of continental restriction to the basin. The moderately high level of bromine in the Mallowa Salt (156·5 ± 43·5 ppm Br for primary halite, 146·1 ± 54·7 ppm Br for secondary halite) accords with evolved continental brines, although highly evaporative minerals such as polyhalite and magnesite are absent. The bromine levels suggest little or no dissolution/reprecipitation of primary halite and yet, paradoxically, there is little preservation of the primary depositional fabric. The preservation of early halite cements and replacement textures supports the idea of an early shutdown of brine flow paths, probably at burial depths of no more than a few metres, and the resultant preservation of primary bromine values in the secondary halite.

Controls and effects of continental brine formation in a supratidal ephemeral lake in the semi‐arid environment of Spencer Gulf, South Australia

Ephemeral saline lakes form along the eastern shore of Spencer Gulf where beach ridges isolate areas of the high supratidal zone. The region is semi‐arid with rainfall averaging about 320 mm/year and with an evaporation rate of 2000 mm/year. Lacustrine sediments in the lake studied contain abundant discoidal gypsum with a calculated δ34S value of +14.9‰ indicative of precipitation from non‐marine, porewater sulphate (δ34S, +13.4‰). Sulphur, deuterium and oxygen isotope distributions and distinctive K/Br and Mg/K ion ratios indicate that groundwaters from landward of and within the lake are non‐marine in origin. The marine‐terrestrial groundwater interface is mobile; after heavy rains, continental‐derived brines flow seaward as far as the high intertidal zone. Within the lake, seasonal changes result in alternate desiccation and flooding by mildly acidic and oxidizing waters. The consequent variability in salinity and redox conditions is inimical to sustained biological activity or sulphide preservation. D...

Continental brines and evaporites of the northern Great Plains of Canada

The northern Great Plains of western Canada contain millions of saline and hypersaline lakes. Although many of the lakes are dominated by Na and SO 4, there is considerable diversity in ionic composition, and nearly every major water type is represented. This chemical diversity gives rise to a surprisingly complex suite of endogenic and authigenic minerals. A wide variety of sodium and magnesium sulfates, carbonates, chlorides, and silicates are present in the modern and Holocene sediments of the lakes. Four distinct types of evaporites can be identified: (a) crusts and hardgrounds, (b) massive and bedded salts, (c) spring deposits, and (d) subsurface and groundwater-related accumulations. The processes responsible for deposition and diagenesis of these evaporites are variable depending mainly on the morphology of the basin and the brine chemistry.

Comparison of composition and concentration of some lagoonal and continental brine lakes

Inland lakes and ocean-bordering natural and artificial salt lagoons were sampled at surface and at different levels where possible. Most were analyzed for five major components Mg, Ca, Na, K, Cl. This paper describes the various lakes and lagoons with regard to their relationship to source of salt, density, concentration, and the chemistry of the water. The ratio of elements to those in seawater were used to trace the balance and the concentration paths. There is an apparent relationship of both hypersaline and hyposaline lacustrine brines to a seawater concentration. This may indicate that seawater, as we know it, could have resulted over time from the progressive concentration of innumerable groundwater discharges.

Evidence from early Proterozoic anhydrite for sulphur isotopic partitioning in Precambrian oceans

Relative to meteoritic sulphur, sulphur in the contemporary exogenic cycle is marked by a depletion of 34S in biogenic sulphide that is balanced by excess 34S in sulphate of the oceans and evaporites1,2. The onset of this isotopic partitioning during the Precambrian required sulphate in the ocean in sufficient concentration to permit significant isotopic fractionation during biogenic reduction3,4; and the evolution of sulphate-reducing bacteria5–7. The conclusion that partitioning existed at 2,300 Myr has been derived from strongly 34S-depleted sedimentary sulphide of this age from South Africa4. I report here on 34S-enriched, stratiform, nodular anhydrite of similar age from Canada, which supports partitioning at this time. Strontium isotope data on these samples indicate that the anhydrite was derived from continental brines, possibly in the inland portion of a continental sabkha. This requires that the reported enrichment in 34S be considered a minimum for seawater sulphate at 2,300 Myr.

Hydrogeochemistry and weathering on the Yilgarn Block, Western Australia—ferrolysis and heavy metals in continental brines

Groundwater samples collected from salt lakes over the Archean Yilgarn Block of Western Australia, show the influence of climate on geochemical weathering patterns. Major element compositions in salt lake groundwaters, show little systematic trend, but there are marked differences in pH and Fe, Cu, and Pb, concentrations in the alkaline carbonated systems of the arid northeastern part, compared to concentrations of the same elements in groundwater systems of the Mediterranean-type climatic region of the “wheatbelt” in the southwestern part of the block. In this latter region, in addition to higher rainfall input, the groundwater systems have steeper hydraulic gradients, weathering bedrock is closer to the surface, and oxidation and hydrolysis of iron (ferrolysis) is evident in weathering profiles. A combination of vertical diffusion and horizontal groundwater flow is thought to be responsible for the development of ferrolysis and acidity in groundwaters in this region. Anomalously high concentrations of heavy metals, particularly lead, are observed in some of the acid-saline groundwaters. The formation of laterite, which is a ubiquitous feature of the Yilgam Block landscape, is a process probably closely linked to ferrolysis.

A stable isotope study of the Mercia Mudstones (Keuper Marl) and associated sulphate horizons in the English Midlands

ABSTRACT Widespread evaporitic sulphate horizons occur in the frequently dolomitic Mercia Mudstones (Upper Triassic) of the English Midlands. The mudstones were deposited on an extensive peneplain which had areas of upstanding minor relief (Charnwood Massif, Derbyshire—Pennines, London Platform). Horst and graben structures formed during the early and middle Triassic, controlled late Triassic sedimentation rates and peneplain slope directions. A stable isotope study (S,C,O) of the sulphates and dolomites of the Trent Formation indicates that during the deposition of the lower Fauld Member grabens such as the Need wood Basin in Staffordshire and areas marginal to a graben such as Newark in Nottinghamshire had a marine brine regime with minor continental input. Using constraints applied by sulphate concentrations of modern waters in arid environments, the ratio of volume of marine input to volume of continental input lay between 3:1 and 4:1. The horst area (East Leake, Nottinghamshire) was strongly influenced by continental brines which derived sulphate from the exposed Carboniferous Hathern Anhydrite Series. A predominantly continental brine regime existed across the whole area during deposition of the overlying Hawton Member. Periodic marine influxes gave rise to thin sulphate horizons whilst continental run‐off was occasionally sufficient to form temporary lakes. The Blue Anchor Formation (Rhaetian) was deposited in a lacustrine environment with waters of mixed marine and continental origin. Salinities were lower than those of the preceding Trent Formation brines.

The composition and origin of brines during the Messinian desiccation event in the Meditterranean Basin as deduced from concentrations of ions coprecipitated with gypsum and anhydrite

Gypsum and anhydrite from the Upper Miocene (Messinian) evaporites of the Mediterranean Basin were analysed for their coprecipitated-ion compositions. The concentrations of Mg, Na, K, Sr and Cl in gypsum and anhydrite samples from DSDP Leg 42a, sites 372, 374 and 376 and from boreholes Yafo-1, Ashdod-2, Talme-Yafe-3 and Afiq-1 from the Coastal Plain of Israel were used to calculate the composition of the brines from which these calcium sulfate minerals were deposited, or in which they have undergone recrystallization or phase transformation. Results reveal basic differences between the eastern, central and western Mediterranean basins during the last stage of the Messinian salinity event. The western Mediterranean and the Ionian Basin were characterized by marine brines during most of the second stage of the salinity event (Upper Evaporite member). During this period the eastern Mediterranean basins were fed with brines of continental origin. These brines are characterized by high Ca concentrations relative to seawater brines. One core from the eastern Mediterranean (Yafo-1) indicated that anhydrite was deposited along the continental margin of the eastern Mediterranean from brines of marine composition, which evolved into Carich continental brines following a marine regression.

Precipitation of Authigenic Minerals in Artesia Group (Middle Permian) Sandstones of Permian Basin: ABSTRACT

Middle Permian Artesia Group sandstones of the Northwestern shelf and Central Basin platform of the Permian basin contain some interesting authigenic minerals (cements) which include clays, sulfates, dolomite, halite, quartz, and orthoclase. To a large degree, diagenetic minerals reflect environments of deposition, although the relation is not always one of cause and effect. Red-brown and red sandstones were deposited in continental depositional environments which include coastal and continental sabkhas and brine pans, eolian plains, and wadis. Deposition of illuviated clay on grain surfaces formed optically oriented cutans (ferriargillans). The red and red-brown coloration reflects iron oxide pigmentation of clay cutans. Formation of ferriargillans was followed by precipitation of sulfates (anhydrite, gypsum, and hemihydrate), dolomite, and halite. The predominant cements are anhydrite and halite which form large crystals that poikilotopically enclose many sand grains. These poikilotopic cements form a very dense matrix which precludes any accumulation of hydrocarbons. Most tan, gray, and white sandstones were deposited in peritidal marine environments. In these sands the following succession of diagenetic minerals was precipitated: (1) quartz overgrowths on quartz grains and orthoclase overgrowths on orthoclase grains, (2) dolomite, and (3) sulfates (anhydrite, gypsum, hemihydrate, celestite, and barite). All effective porosity and permeability are in dolomite cements which consist of tiny rhombic crystals. Anhydrite is the predominant sulfate cement and, as in continental sandstones, occurs in large crystals and very dense poikilotopic fabrics which preclude migration of hydrocarbons. The critical factor which controls the economic potential of these sands is the relative proportion of porous, permeable dolomite cements to nonporous anhydrite ceme t. End_of_Article - Last_Page 474------------

Sulfur and Oxygen Isotope Geochemistry of Abu Dhabi Sabkha: ABSTRACT

Sulfur and oxygen isotope data vary in a laterally systematic manner across the sabkha at Abu Dhabi. At least three different mechanisms are required to explain the variation of ^dgr34S and ^dgr18O of sulfate in evaporite minerals and interstitial brine. Gypsum is precipitating in the seaward zone, and extensive postcrystallization exchange maintains isotopic equilibrium between bulk gypsum and dissolved sulfate. Anhydrite is the dominant sulfate mineral in the central zone where bacterial sulfate reduction results in heavier ^dgr34S and ^dgr18O values. In the landward zone both minerals and brine reflect mixing with the isotopically distinct sulfate of continental brines. Laterally systematic isotopic variation supports Patters n's chemical discrimination between seaward, mixed and landward hydrologic regimes, and is consistent with vertical variation of ^dgr34S demonstrated by Butler et al for this regressive sedimentary sequence. Gypsum-anhydrite transitions do not have significant effects on the isotopic composition of sulfate. Some ancient marine evaporite formations consisting mainly of dolomite and anhydrite may have formed in environments similar to the seaward and central zones of the Abu Dhabi sabkha; considerable isotopic variation would probably accompany subaerial deposition of laterally extensive marine evaporites. End_of_Article - Last_Page 505------------

Petrography, Geochemistry and Factor Analysis of a Lower Ordovician Subsurface Sequence, Tasmania, Australia

ABSTRACT :Thirty-two limestone facies, four dolomite facies and 10 terrigenous clastics facies show wide variation in a short distance of 600 meters. The limestones represent subtidal (biofacies), tidal channels (oolite facies), bar (oncolite facies), intertidal flats (algal facies), supratidal early diagenetic dolomites and secondary dolomites. Terrigenous clastics were deposited in environments ranging from intertidalsupratidal flats, coastal dunes and subtidal to supratidal flats, coastal dunes and subtidal to supratidal channels. Strontium and Na define the limestone facies and salinity variation. Dolomitizing brines were saline and contained three times more Mn than the depositional solutions. Manganese and Ba in the dolomites indicate mixing of continental and marine brines during dolomitization. Early and late diagenetic chemical imprints are preserved despite prolonged meteoric diagenesis. The carbonate dendrogram depicts four distinct clusters and facies variation related to subtidal, intertidal, supratidal depositional environments, diagenesis and dolomitization. Factor score plots show distinct environmental gradation (from open marine conditions towards the east and restricted marine towards the west) and porosity evolution. Increase of salinity from east to west establishes the continuity of the depositional solutions. Chemical variation of dolomites delineates lateral continuity in the early and late movement of dolomitizing solutions which were generated in the west and moved eastward. The terrigenous clastics dendrogram depicts six distinct clusters corresponding to intertidal-supratidal flats, coastal dunes and subtidal to supratidal channel environments and the diagenetic changes related to silica cementation, dolomitization, iron-coating and mica growth. Factor score plots show gradation of these depositional and diagenetic environments. The type of porosity is fabric selective. The amount of porosity is facies controlled and it is not related to the core recovery.

Concentration of Potash Salts in Saline Basins

Commercially valuable potash salts such as sylvite and langbeinite generally occupy only small parts of evaporite basins, whereas noncommercial potassium-bearing minerals such as carnallite and polyhalite are of more widespread distribution. The processes of concentration of potassium salts probably begin shortly after salt first is precipitated within the basin. As brine is concentrated, very complex solutions are formed which influence the chemical and physical factors of concentration. Environmental and geologic processes at this time further restrict the locations in which the potash-bearing solutions can precipitate. Upon complete evaporation of the seawater and burial of the preserved complex salts, potash salts may be concentrated further and enriched by metasomatic processes. Salts now are precipitating on a reduced scale in limited areas along the continental margins of the ocean basins, inland seas, continental brine lakes, and salt pans. Trace minerals, such as bromine, cesium, and rubidium, are of special interest in saline studies, because they furnish much information on the genetic character of the salts. Argon, commonly found within salt measures where a high concentration of potassium is present, is an element that can be used to determine the age of the salt.

Considerations Regarding Formation of Potash Deposits: ABSTRACT

Commercially valuable potash salts usually occupy only minor parts of evaporite basins, whereas certain noncommercial potassium-bearing minerals have a more widespread distribution. The processes of the concentration of these potentially valuable salts no doubt begin when salt first is precipitated within the evaporating basin. As brine concentration increases, highly complex solutions are formed which influence not only the chemical but also the physical factors of concentration. Environmental and geologic processes at this time further aid in restricting the depositionally favorable locations in which the potash-bearing solutions can precipitate. On completion of evaporation and burial of the preserved complex salts, further concentration and enrichment of the potash salts may occur due to metasomatic processes. Saline precipitation presently is taking place on a reduced scale in some locations along the continental margins of the ocean basins, inland seas, continental brine lakes, and salt pans. Trace minerals, such as bromine, cesium, and rubidium are of special interest in saline studies, because they furnish much information on the genetic character of the salts. Argon, found commonly in salt sequences where a high concentration of potassium is present, aids in the determination of the age of the salt. End_of_Article - Last_Page 529------------