Conductive zones in the Territory

What a way to finish! I spent a lot of time this week looking at thin sections from a fascinating ore deposit (more to come about that later...). But this afternoon I swapped scales and ended the week thinking about the fabulous Northern Territory. I plotted the AusLAMP magnetotelluric depth slices published by Geoscience Australia, combined these with gravity gradient strings published by Northern Territory Geological Survey and made a map for you! Let's have a look together at some of the interesting features.

In the 33km depth slice, corresponding approximately to the base of the crust the NT is riddled with ridges of conductivity, and these conductive zones seem to nicely match the deeper gravity worms. By the time we reach the mid-upper crust at 10km, a lot of the conductive ridges have disappeared, and we're left with a lot more high frequency variation in conductivity.

Let's compare a few of the key mineral fields. In the Tanami, conductivity seems to span the whole crust. Tennant Creek has a lower conductivity response in the shallow depth slice. Jervois seems to lie between two deeper conductivity ridges, and proximal to but offset from a shallower conductivity zone. McArthur River (Teena) seems to be modestly conductive through the whole crust, but conductive nonetheless.

I would love to know why! These different mineral systems seem to be related to variations in conductivity which, I presume reflect things like the temperature and source of magmatism (if present), composition of ore forming fluids, degree of later overprinting, depth and age of cover sequences... What other things can you think of that could cause these whole of crust variations?

There are also clear zones that are extensions of these features but which don't have major deposits known on them. Are they also fertile...? So many questions!

Anyways, after that excursion through the crust, it's back to the thin sections for me next week, but I'll be changing from a deposit to a prospect - less sulphides and more silicates. My thanks to the fantastic companies I am having the pleasure of working with these days. This consultant life indeed!