Anyonewho thinks this stratigraphic drilling on NDIBK04 has...

Anyonewho thinks this stratigraphic drilling on NDIBK04 has thrown us up a dud needs to look at the big picture to understand what is now known about the region. The AGES abstracts are now available for public viewing.

https://geoscience.nt.gov.au/gemis/ntgsjspui/handle/1/92054

Peopleshould read the paper “Shining new light on the(previously) dark depths of the East Tennant region” commencing on page 115 to get a betterunderstanding of what the experts are now able to confirm as a result of thedrilling campaign, not just on NDIBK04 but also holes 1 -10.

I have copied some of the mostpertinent comments made on NDIBK04. Bolded sections have been done by me.

“BoreholeNDIBK04 was drilled into the hanging wall of the southeast-dipping Lamb Fault(Figure 1) and intersected the oldest rocks known from the East Tennant region.Sparse zircon from deformed, predominantly pelitic metasedimentary rocksyielded a unimodal date of ca 1969 Ma. These are overlain by a lithologicallydiverse package of metacarbonate and fine-grained siliciclastic metasedimentaryrocks that yielded more abundant zircon, which gave an unimodal date of ca 1894Ma. Although both are strictly maximum ages for deposition of the supracrustalprecursors, the uniformity of the age distributions and the euhedralmorphologies of the zircon crystals and fragments implies first-cycle erosionand short sedimentary transport distances; this suggests these ages areapproximate true stratigraphic ages.

This age of stratigraphy has not beenrecorded in the Tennant Creek area or the Murphy Province and is unique toborehole NDIBK04; therefore, the regional extent of pre-1890 Ma supracrustalrocks is unknown. They may be spatially restricted, or they may representan older sedimentary succession that underlies the Alroy Formation (see below)and Warramunga Formation in the East Tennant region and the Tennant Creek arearespectively.

Stratigraphicdrilling has yielded a wealth of new data, the interpretation of which, inconjunction with geophysical data, has important implications for mineralsystems prospectivity in the East Tennant region as a number of key elementsrequired for the formation of large mineral deposits have been identified.

Wenow recognise that felsic magmatism in the East Tennant region is far morevoluminous than previously interpreted, and that plutonism drove elevationof the regional thermal regime at 1855–1845 Ma. In addition, Jiang et al (2022;see also Figure 3) identified previously unrecognised major structures thatshow evidence for crustal-scale fluid flow in the East Tennant area, providinga conduit for transport of metals, fluids and ligands from depth. Finally, oredepositional gradients (eg chemically reactive rocks and redox boundaries:Schofield et al 2020; Clark et al 2021a) are present in the near-surface,providing potential locations for metal precipitation. Moreover, thestratigraphic drilling has demonstrated direct evidence for mineral systems inthe East Tennant region as shown by mineralisation intersected in boreholeNDIBK04. Syn-deformational quartz-sulfide veins are common, with sulfidesdominated by pyrrhotite at depth and pyrite at shallower levels, and with minorsphalerite and chalcopyrite. Discrete zones have gold–arsenic–copper–zinc–silver–bismuth mineralisation hosted by variably graphiticmetasedimentary schists with maximum depositional ages of >1890 Ma.

Thegold mineralisation shares some geological and geochemical features with iron[1]sulfide copper–gold (ISCG) or base metal-rich orogenic gold deposits (Skirrow et al in prep). We interpret mineralisation to be synchronous with D2 deformation based on detailed petrographic observations. Broader comparisons suggest that this mineralisation could be similar in timing to gold–copper–bismuth mineralisation in the Tennant Creek goldfield and gold mineralisation elsewhere in the North Australian Craton (Skirrow et al in prep).

So we nowhave a previously unknown age group of rocks to the region . What is thistelling us in regards to our targets?

We now haveconfirmation that magmatism in the area is larger than previously thought.

The goldmineralisation is similar in timing to the Tenant Creek event. On that point, Hole DDH005 which is some 35klms to the west of NDIBK04 also had trace gold values so mineralisation may be more widespread than previously thought.

There is alot to like about what these results are indicating – we just need Inca to hone in on the source of the mineralisation. I suspect that will occur sometime this year.