Fathom Geophysics Newsletter 26

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Exploration News: Thick mafic volcanics found beneath McArthur River deposits

Thick basal sequences of mafic volcanic rocks have been implicated in the formation of sediment-hosted base metal deposits in northern Australia's McArthur Basin.

The findings appear in a journal paper by CSIRO and Northern Territory Geological Survey scientists. [1]

Australia's McArthur Basin is part of a broad sediment-hosted zinc-lead-silver province that hosts the McArthur River (HYC), Century, and Mount Isa deposits.

The McArthur Basin area was thought to have developed in a distal continental back-arc setting that experienced numerous crustal extension and shortening events.

"Exploration for sediment-hosted base metal deposits requires a strong knowledge of the structural architecture of a basin," the scientists said in their paper.

Datasets they used to interpretively map lithologies and structures in the southern McArthur Basin included gravity, airborne magnetic, airborne electromagnetic, and radiometric surveys published between 1989 and 2018. They also made use of seismic reflection survey data collected within the region.

They used potential field data to construct forward-modelled regional-scale geological cross sections within the southern McArthur Basin study area. To help constrain their cross-section models, they used additional information that included (1) petrophysical data obtained by other researchers from legacy drillcore, (2) previously mapped geology and structure from 1:250K map sheets, (3) gradients in gravity and magnetic data, and (4) seismic data and wells.

As part of their work they also used their interpreted geology maps and their modelled cross section results to reconstruct how the southern McArthur Basin evolved in response to tectonism in the region.

The researchers found a close spatial association between known base-metal occurrences in the central Batten Fault Zone, including McArthur River and Teena mineralization, and unusually thick sequences of mafic volcanic rocks within the basin's Tawallah Group, which represented early basin fill.

They said that assuming these mafic units were the source of deposits' base metals, deep-tapping faults found in the area "would have provided a direct pathway for [basinal brine] fluid transport from the source region to organic-rich and pyritic mudrocks of the Barney Creek Formation as the trap."

"The presence of this large volcanic pile, which is intersected by several deep-seated faults, is likely one reason why the central Batten Fault Zone is so well endowed with zinc-lead-silver mineralization."

They said that geophysical studies similar to what was carried out in the McArthur Basin could be used to help assess the extent of any volcanic units present in other basins prospective for sediment-hosted base metal mineralization — if a spatial association between volcanic units and targeted mineralization was known or inferred in those other basins.

References

[1] T.N. Blaikie and M. Kunzmann (July 2020) "Geophysical interpretation and tectonic synthesis of the Proterozoic southern McArthur Basin, northern Australia", Precambrian Research, 343, 105728.

About Fathom Geophysics

In early 2008, Amanda Buckingham and Daniel Core teamed up to start Fathom Geophysics. With their complementary skills and experience, Buckingham and Core bring with them fresh ideas, a solid background in geophysics theory and programming, and a thorough understanding of the limitations of data and the practicalities of mineral exploration.

Fathom Geophysics provides geophysical and geoscience data processing and targeting services to the minerals and petroleum exploration industries, from the regional scale through to the near-mine deposit scale. Among the data types we work on are: potential field data (gravity and magnetics), electrical data (induced polarization and electromagnetics), topographic data, seismic data, geochemical data, precipitation and lake-level time-lapse environmental data, and remotely-sensed (satellite) data such as Landsat and ASTER.

We offer automated data processing, automated exploration targeting, and the ability to tailor-make data processing applications. Our automated processing is augmented by expert geoscience knowledge drawn from in-house staff and from details relayed to us by the project client. We also offer standard geophysical data filtering, manual geological interpretations, and a range of other exploration campaign-related services, such as arranging surveys and looking after survey-data quality control.