Inverted Hunder dune swales, Ladakh, India

J. D. A. Clarke1 and S McGuirk1, 2

1Mars Society Australia, c/o 43 Michell St Monash, ACT 2904; 2Fenner School, Australian National University, ACT 0200

Introduction

The Hunder Dunes are one of a series of small dune fields in the Shyok and Nubra valleys of the Ladakh region of north-western India.  The dune fields are composed of mostly barchanoid and transverse dunes and are composed of sand reworked from the seasonally exposed beds of these rivers.  Wind directions are strongly uni-modal in orientation and controlled by valley orientation (McGuirk 2017).  The Hunder Dunes occur at an altitude of 3083 m in the Nubra valley and cover an area of about 1500 x 700 m.  The area is a popular tourist location because of the visual impression of the dunes against the background of the Karakorum Range rising to over 6000 m, and the presence of a small herd of Bactrian camels. No scientific investigation of the dunes have been previously made. During a 2016 expedition to the area (Pandey et al. 2019) we noticed the presence of numerous inverted swale deposits. Inverted swales have not, to our knowledge, been described in the literature. We here present a brief description of them, and discuss their formation and possible significance.

 Location

The Hunder Dune field occurs in the Nubra valley and are centred at 77°29’47.60″E and 34°34’49.00″N.  The dune fields are composed of mostly barchanoid at the present time, although the evidence from Google Earth imagery shows that they have been dominated by transverse bedforms in the past.  The dunes lie on the south bank of the Nubra River The Hunder Dunes occur at an altitude of 3083 m in the Nubra valley and cover an area of about 1500 x 700 m

Climate

The climate of the Hunder Dunes is arid with warm summers and cold winters, temperatures falling below zero.  The area corresponds with zone IV of Hewett (1989).  Valley floors experience strong winds, the dominant wind vector responsible for the dunes is from the northwest.  No rainfall data exists for Hunder, but the city of Leh in the valley of the Indus, which is the next valley to the south, has an annual rainfall of 104 mm (Climate data 2018).

Morphology and stratigraphy

The features interpreted as inverted swales consist of small (10-20m long, 5-10m wide, and up to 1.5m high), ellipsoidal mesas exposed in the swales between active dunes.  Most of the mesas have a tiered, wedding cake appearance, due to the presence of stacked cycles of sediment (Figure 2). Individual cycles range from 40 to 50 cm in thickness, and are composed of a repeated succession of lithologies (Table 1), forming cycles. Not all units are present in each cycle, unit A is only present only at the base of the mesa, and is not always exposed. Only one of the rippled units B and C may be present, and rarely the muddy unit D is absent. Some swales are partly buried by dune migration, some others are being exposed by the same process.

Interpretation

As shown in Table 1, the cyclic units are interpreted as showing the flooding of dune swales by muddy river waters, followed by their desiccation.  The convex-upward basal unit A represents the aeolian swale deposits.  The convex upward geometry of the swale is propagated ward through each cycle. The asymmetric cross-laminated unit B represents the influx of river flood water carrying sand and mud.  The symmetric cross-laminated unit C represents wind-driven wave sand deposition water flood recession as isolated the sales into ponds.  Interference patterns between ripple sets are visible on the upper surfaces of the topmost cycles exposed in the mesas.  The uppermost unit C represents settling out of suspended mud in the final phases of drying out of the pond in the swales.  The muddy unit is often desiccation cracked and may preserve vertebrate footprints. Multiple cycles of flooding and desiccation form the swale deposits.

The deposits are very weakly indurated following deposition by precipitated carbonate.  This allows them to withstand deflation to form the mesas.  The muddy unit C is also slightly more resistant than the sands to erosion, so form overhanging caps.  The mesas show small scale landforms showing wind erosion, including polished surfaces and ventifacts (Figure 5).

Discussion

Several swales in the Hunder dunes were flooded at the time of our visit.  These ponds lacked mud, however, so we interpret the water as being due to either a raised groundwater table, or rainfall runoff, or both.  The sale flooding from the river would carry mud, as the suspended sediment load of the Nubra River is substantial.

While the dune swales can be flooded by the Nubra River we expect the deposits to accrete to the height of the river flood.  When isolated from the river by dune migration, erosion of the swale deposits can begin, leading to formation of the concave upward wedding cake inverted mesas


Biography

Jonathan Clarke has more than 40 years professional experience in industry, government and university sectors He is an associate of the Australian Centre for Astrobiology, Adjunct faculty of the Amity Centre of Excellence in Astrobiology, and post-graduate instructor in astrobiology at Swinburne University

Soil geochemistry imaging gold prospectively in the South West Terrane of Yilgarn Craton, Western Australia

De Souza Kovacs, Nadir1 and Lu, Yongjun1

1Geological Survey of Western Australia, Perth, Australia

The South West Terrane of the Yilgarn Craton is prospective for a number of important commodities such as gold, nickel and lithium; however, the region remains poorly geologically understood. The South West Terrane is one of the focus areas of the Geological Survey of Western Australia’s Accelerated Geoscience Program, 2020–21. This terrane is often associated with farming land, viticulture and grain growing; nevertheless it also hosts several word-class mineral deposits such as those at Boddington (Au–Cu), Greenbushes (Li–Ta) and Ravensthorpe (Ni). The geology of these deposits known from open-file statutory exploration reporting (stored in the Geological Surveys MINEDEX and WAMEX databases) provide a wealth of knowledge, that when combined with other publicly available geoscientific data compiled by the survey, data are providing new insights into the geological and mineralisation histories of the terrane.

The gold assay results from 84157 soil samples covering the South West Terrane were extracted from WAMEX and were spatially visualized and evaluated. The distribution of high-grade gold samples (0.53 to 1.37 ppm) cluster along several regional faults, including the Newdegate, Darkan, Manjimup, Tenterden, Koolanooka, Hyden, Pingarning, Dumbleyung Faults and other prominent but unnamed regional faults. By contrast, low-grade gold (<0.001 ppm) samples occur in areas without major faults. The regolith-landform map shows that the southern part of the Lockhart Paleovalley follows the strike of the Newdegate Fault and coincident structures on regional-scale magnetic images. The spatial distribution indicates that gold in soils is genetically linked to the regional faults, which are likely to have acted as fluid pathways during gold mineralization.

One particularly interesting feature is that high-grade gold in soils clustering along the north-trending Newdegate Fault also coincide with the isotopic boundary imaged by whole-rock neodymium isotopes of felsic igneous rocks. This isotopic boundary also correlates well with gravity and magnetic anomaly zones, and has been suggested to be the terrane boundary between the South West Terrane and the Youanmi Terrane (Lu et al. 2021 AESC). This correlation is supported by the spatial distribution of gold deposits including Griffins Find, Tampia and Edna May which are located on or close to this isotopic boundary. It indicates that gold anomalism in soils might be potentially useful for ranking deep crustal structures.

The spatial distribution of gold in soils in the South West Terrane is closely associated with regional faults. Through integration with other data, such as isotopic mapping or regional geophysical compilations, the regional scale gold in soil datasets can assist in prioritising the most prospective areas for exploration.


Biography

Nadir de Souza Kovacs is a Senior Regolith Geologist at GSWA, she has compiled several regolith maps including the State Regolith Map of Western Australia. Dr. Yongjun Lu is a renowned Senior Geochronologist Isotope Geologist at GSWA. He received the Waldemar Lindgren Award of Society of Economic Geologists in 2018.

Hydrogeochemistry to explore the Georgina Basin’s phosphate potential

Schroder, Ivan1; de Caritat, Patrice1

1Geoscience Australia, Canberra, Australia

With the increasing need to extend mineral exploration under cover, new approaches are required to better understand concealed geology, and to narrow the mineral prospectivity search-space. Hydrogeochemistry is a non-invasive exploration technique based on the premise that groundwater interacting with a deposit or supergene alteration can cause anomalous elemental and isotopic signatures down-gradient. Water chemistry can reflect mineralisation directly, but can also reveal other key components of a mineral system, including fluid-flow pathways (e.g. fault/fracture zones), evidence for mineral system traps (e.g. evaporites, shales), or metal sources (e.g. mafic rocks).

The Northern Australia Hydrogeochemical Survey (NAHS) was a multiyear regional groundwater sampling program that aimed to understand the regional mineral potential within the Tennant Creek to Mt Isa area (Schroder et al. 2020). This presentation will explore the application of NAHS for investigating mineral potential of a region and present a workflow for establishing spatial or lithological baselines to evaluate hydrogeochemical anomalies.

The Georgina Basin is well known for its phosphate potential, with several >1 Mt deposits discovered in recent years such as Amaroo and Wonarah; however, the basin has been largely unmapped in terms of phosphate distribution under cover. This work focuses on a subset of 162 NAHS samples collected within two predominant aquifers of the Cambrian Georgina Basin (and time equivalents in the Wiso Basin). This focus restricts us to samples which experience a similar climate, recharge conditions, and aquifer compositions, reducing the hydrogeochemical variation that can mask intra-aquifer anomalies.

Elevated concentrations of P (used as a proxy for PO43- and normalised to HCO3 or Cl) is observed in the groundwater on the eastern margin of the Georgina Basin. This region is known for Cambrian phosphorite deposits, with sampled bores proximal to a number of near-surface Georgina Basin phosphorite deposits. Additionally, several other subgroups within the Georgina Basin were identified with elevated P, corresponding to areas of greater cover and without known phosphorite deposits nearby.

Because the solubility of phosphate minerals depends on many factors — including groundwater physicochemical parameters (pH, T etc.), groundwater chemical composition, and phosphate mineral composition (such as degree of CO32- substitution) — a high (or low) P concentration is not a definitive indicator of the presence (or scarcity) of phosphates in the aquifer or recharge area. Thus, our data analysis focused on minor (i.e. F) and trace (i.e. U, V) elements commonly substituting in phosphate mineral structures or typically enriched in phosphorites, to evaluate these elements’ relationships with P concentration as a tool for recognising dissolution of phosphate-bearing minerals. When normalised to Cl on log-log scatterplots, clear linear relationships between selected minor/trace elements and P concentrations become apparent in several of the identified subgroups that cannot be attributed to other water-rock interactions. This observation supports the implication that there is further undiscovered regions of the Georgina Basin with potential for hosting phosphorites.  

References

Schroder, I.F., Caritat, P. de, Wallace, L., et al., 2020. Northern Australia Hydrogeochemical Survey: Final Data Release and Hydrogeochemical Atlas for EFTF. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2020.015  


Biography

Ivan is a geochemist within the Mineral Potential of Australia Section of Geoscience Australia. His focus in recent years has been on hydrogeochemistry and it’s application to mineral exploration. He has been an instrumental part of the Northern Australia Hydrogeochemistry Survey project which he will present on today.

Regolith-Hosted Ferrihydrite: A Forgotten Sorbent in the Search for REE’s?

Tobias Bamforth 1,2, Caroline Tiddy 1, Ignacio Gonzalez-Alvarez 2,3, Eric Whittaker 4, Leon Faulkner 5

1Future Industries Institute (FII), University of South Australia (UniSA), Adelaide, Australia; 2CSIRO, Mineral Resources Discovery Programme, Kensington, Perth, Australia; 3CET, University of Western Australia, Crawley, Perth, Australia; 4Terramin Australia Ltd., Adelaide, Australia; 5Environmental Copper Recovery Ltd., Adelaide, Australia

The negatively-charged surfaces of clay minerals demonstrate an excellent capacity for the adsorption of rare-earth elements (REE’s) in regolith. Often, this is observed during the formation of secondary phases such as kaolinite and halloysite (Borst et al. 2020. Nat. Comm.), though alternate clay minerals display a similar capacity for REE sorption across low-temperature environments. For instance, ferrihydrite (5Fe2O3 · 9H2O) is an amorphous clay mineral that is widely acknowledged as an excellent REE sorbent in hydrospheric systems. Thus far, evidence for its potential in association with high-grade REE accumulation has been limited; however, new data from the Kapunda Cu mine, South Australia, suggests that even in the presence of co-existing kaolinite, ferrihydrite may act as a principal sorbent during lanthanide fixation. 

Petrographic analysis of weathered vein samples from the Kapunda mine, which exhibit total rare-earth oxide (TREO) concentrations of 17.1 wt%, demonstrate that interstitial aggregates of REE phases monazite and rhabdophane are spatially associated with ferrihydrite particulates. In comparison, a negative correlation is observed between REE minerals and crystalline phases of goethite, hematite and kaolinite. Ferrihydrite formed during the acidic dissolution of primary pyritic minerals, which is evidenced by cubic void spaces throughout the sample. In addition, geochemical evidence from Ce/U valency modelling suggests that weathering fluids were highly acidic (pH 1 – 3) and moderately oxidising (Eh 0.7 – 0.9) in nature. REE mobilisation was likely facilitated by the formation of sulphate complexes, which is supported by geochemical whole-rock profiles that exhibit low chondrite-normalised La/Yb ratios (Migdisov et al. 2016. Chem. Geol.). Chondrite-normalised plots also exhibit Pr > Nd > Ce > La enrichment, which compliment previous conclusions on the ability of ferrihydrite to selectively adsorb the valuable REE’s Pr and Nd (Bau. 1999. Geochim. Cosmochim. Acta.). Phosphate ions were sourced from primary sedimentary apatite, which is evidenced by the pseudomorphic replacement of hexagonal crystals by secondary REE-baring phases. This advocates for the role of ferrihydrite as a catalyst following the co-adsorption of REE’s and PO42- (Arai and Sparks. 2001. J. Colloid Interface Sci.), and explains the observed spatial boundaries of lanthanide accumulation, as apatite is not expressed in notable quantities throughout the bulk of the Cu deposit.

Results demonstrate the potential of ferrihydrite as a principal sorbent for economic REE mineralisation, when considering: (1) its relative pervasiveness across global regolith profiles; (2) its crystal structure, surface area and adsorption capacity and; (3) its potential ability to selectively adsorb the valuable light rare-earth elements Nd and Pr. Additionally, this work emphasises the importance of apatite as a phosphate source in REE-mineralising systems, and advocates for the increased consideration of ferrihydrite as a potential catalyst for REE accumulation as the demand for these critical metals escalates under the development of renewable technologies.


Biography

Tobias studied BSc Geology at the University of Southampton, before completing an MSc in Global Management of Natural Resources at University College London. During this time, he completed a mineral exploration studentship at UniSA and CSIRO, and is now studying a PhD in Geochemistry at Murdoch University, Perth.

Martian regolith: from cryolithosphere to atmosphere

Caprarelli, Graziella1

1Centre for Astrophysics, School of Sciences, University of Southern Queensland, Toowoomba, QLD 4350, Australia

Regolith is: “everything, from fresh rock to fresh air”1. The term indicates the layers of loose material that mantle bedrock, although there is disagreement among regolith experts between the camp that subscribes to the broad definition given above, and the camp that discriminates between the material formed in place as a product of weathering, and sediments formed elsewhere, transported and deposited on bedrock which was not the parent material2. We now know that regolith mantles the surface of all rocky bodies in the solar system: on many of these objects there are no geological processes leading to sedimentary erosion and deposition such as on Earth. Thus, here I use the term in its broader sense.

Mars is a hyperarid planet3, with water stored as ice in its polar caps and in the ground. The uppermost layers of the martian crust are thus termed the ‘cryolithosphere’. Meteoritic “gardening” since early Noachian times (~ 4.0 Ga) has produced the thick layer of broken rocky material covering Mars’s surface globally. Wind erosion and mass wasting also act on a global scale, while chemical processes have led to the deposition of hydrous minerals in the soil. The martian regolith thus comprises dust, sandy soils and sediments, pebbles, rocks, secondary minerals, and may include water ice at mid- to high latitudes, where permafrost landforms are observed4, and where additional disintegration of bedrock occurs owing to thaw/freeze cycles. Aeolian processes move solids across the martian surface: dust particles (< 10 mm) may remain in suspension indefinitely; dust and silt (< 60 mm) are lifted and may be deposited at great distance by atmospheric currents; sand particles (up to a few hundred mm) move by saltation, breaking into smaller fragments that may then be lifted; coarse grained material (1-5 mm in size) is dragged or accumulates as lag deposits. A way to study the distribution of these materials is through satellite thermophysical data: mapping based on thermal inertia and albedo classification5 shows links between type of material and geology.

My colleagues and I have investigated the spatial distribution and vertical composition of the martian cryolithosphere through impact processes6 and by ground penetrating radar7. Here, I show and discuss the main outcomes of our work in relation to: (a) the spatial distribution of the martian regolith and its composition; (b) ground ice and regolith; (c) the link between cryolithosphere and atmosphere. These aspects underpin part of the geological and climatological history of the planet, with far reaching implications about the selection of landing sites and possible future human missions to Mars.       

1Eggleton RA, Ed. (2001) CRC LEME, ISBN 0-7315-3343-7, 144 pp.

2Pain and Ollier (1996) AGSO J Austral Geol Geophys 16(3), 197-202. 

3Baker VR (2001) Nature 412, 228-236. 

4Lasue et al. (2013) Space Sci Rev 174, 155-212.

5Jones et al. (2014) Remote Sensing 6, 5184-5237.

6Jones et al. (2016) JGR Planets 121, 986-1015.

7Orosei et al. (2017) JGR Planets 122, 1405-1418.


Biography

Dr Graziella Caprarelli FAIG is Adjunct Research Fellow with the Centre for Astrophysics at the University of Southern Queensland, Adjunct Research Professor at the International Research School of Planetary Sciences (Italy), and member of MARSIS science team. She explores the martian subsurface geology looking for water.

About the GSA

The Geological Society of Australia was established as a non-profit organisation in 1952 to promote, advance and support Earth sciences in Australia.

As a broadly based professional society that aims to represent all Earth Science disciplines, the GSA attracts a wide diversity of members working in a similarly broad range of industries.