In archaeometallurgy, Pb isotopes are the method of choice to link Pb-bearing artefacts with Pb-bearing deposits. Galena is not a common detrital mineral in stream sediments. But it can survive some fluvial transport as being armored with rimes of cerussite which is more resilient than its predecessors galena and anglesite. Since these supergene alteration does not modify the Pb isotope ratios this approach deemed to be a successful one. I myself only used Pb isotope ratios in galena and in cerussite deposits themselves for genetic purposes.

The other option , the use of Pb isotopes in lithochemical exploration may provide also good results. These Pb isotope fingerprings approaches can hardly be applied to grassroot exploration because of the need of reference material for certain mining districts. For me it seems to be a bit of an awkward way of exploration. There are more cost-effective and less time-consuming ones.

HGD

As with all geological systems you need to understand the data and let the data inform the interpretation, not make an interpretation then use the data to support it.

Many studies have reported Pb-isotope analyses with the data used to: develop standards, global and terrain-specific growth curves and dating techniques (Cooper et al. 1969, Cumming & Richards 1975; Stacey & Kramer 1975, Gulson 1984); to distinguish between groups of deposits within a single terrain (Stanton & Russel 1959, Cannon et al. 1961, Gulson & Mizon 1979, Gulson et al. 1985, Carr et al 1995 etc); and, to highlight the time difference between lode formation within a single system (Broken Hill, Pinnacles; Parr et al. 2004).

Lead isotope studies can provide insights into tectonic and mineralising events and improve the understanding of events within a given terrane (Carr et al 1995, Huston et al 2016). Major magmatic, thermal and hydrothermal events typically result in the loss of 238U, 235U and 232Th and homogenise Pb isotope values unless overprinted by later high-Pb events, or by the addition of radiogenic Pb (Doe & Stacey 1974; Faure & Messing 2005). The addition of radiogenic Pb may modify the initial ratio of a sample, leading to Pb isotope signatures higher than the initial (primary) ratio (Cannon et al. 1961). In high-Pb samples, including galena and samples with >700 ppm Pb, there is generally insufficient 238U, 235U and/or 232Th present to significantly change the “initial” Pb-isotope value through radioactive decay (Gulson 1986) 9although there are exceptions - the MVT mineralisation in the Adelaidean overlying the palaeoproterozoic Broken Hill area). By contrast, for low-Pb samples the breakdown of even small amounts of 238U, 235U and/or 232Th may (and often will) significantly change the “initial” Pb-isotope ratio and such samples need to be treated with caution.

Pb isotope data is a powerful tool in the identification and discrimination of mineral systems. However, you need to understand what you are trying to establish. For example, If you are trying to discriminate between gossans and/or high Pb soil anomalies resulting from the weathering of mineralised veins vs false anomalies resulting from weathering related processes you need to have data from both the target system as well as the zones that you are interested in (see Gulson 1986 and related papers). However, as clearly demonstrated in a recent paper by Fitzherbert et al (2019) for the Cobar Basin NSW Australia, you need to be careful. New dating of mineral systems in the Cobar Basin supported by high precision Pb and other isotopic data has clearly shown that instead of a single mineralising event there was a near continuous series of events with mineral systems evolving and telescoping, often within the same structure over a 40 My period with epithermal > intrusion related Cu-Au > reduced basinal fluid Pb-Zn systems with systems migrating spatially over time. It took the combination of high precision dating using several techniques together with high precision Pb isotope data to resolve the what was happening over a +150km zone that hosts a massive amount of metal.

Having worked on many Pb isotope datasets over a 30 year period, some words of caution:

• Don't assume there is only one mineralising event within the area, that has yet to be demonstrated
• Where possible get new/recent Pb isotope analyses for the target system(s) rather than rely on old published analyses. There are several reasons for this including:

Peter

Carr G.R., Dean J.A., Gulson B.L. & Suppel D.W.1991. Lead isotope signatures of Ordovician to Permian mineralisation in the Lachlan Fold Belt — genetic and exploration implications. Geological Society of Australia, Abstracts 29, 6.

Fitzherbert J. A., Downes P. M., Blevin P. L., Huang H., Matchan E., Waltenberg K., Wall C. & Phillips D. 2019. Refining the Cobar-type mineral system: new insights spawned from direct dating of mineralisation. Discoveries in the Tasmanides 2019 (Mines and Wines 2019), AIG Bulletin 69

Gulson B.L. 1986. Lead isotopes in mineral exploration. Amsterdam, Elsevier, 245 pp.

Huston D.L., Champion D.C., Mernagh T.P., Downes P.M., Jones P., Carr G., Forster D. & David V. 2016. Metallogenesis and geodynamics of the Lachlan Orogen: new (and old) insights from spatial and temporal variations in lead isotopes. Ore Geology Reviews 76, 257–267