How Hot Is Hot?

[Off Grid]

Full disclosure here, I'm a data junkie, but whenever I see reference to hot ground I wonder if anyone has ever put together a simple method of measuring hotness? I guess that would be in WA if anywhere? I realize that there's many factors involved as Minelab's great introduction below discusses. If you set aside salt beaches and wet clay and just consider dry-land detecting would the percentage of magnetite, or whatever a magnet picks up (ilmenite, maghemite) be a reasonable measure of hotness? If so, what percentages would constitute  low mineralization thru hot mineralization ?

https://www.minelab.com/__files/f/11043/KBA_METAL_DETECTOR_BASICS_&_THEORY.pdf

[Steve Herschbach]

 

[Aureous]

I've often heard reference to people in WA say 'we've got the hottest ground' and I've detected in every state except Tas and Qld and I can honestly say that Vic and SA have the worst 3 spots I've ever seen. In WA, I've detected ground from the Kimberley, all the way down to Norseman and apart from salt mineralization, the Pilbara had the worst in that state. For a sheer barrier, the ground at Salvation Hill near Dunolly is by far the worst. A detector shop used to have a slab of dirt from there on the counter which was arc-welded together....it was maybe 70% iron! You'd be lucky to get a few inches depth on a multi gram nugget there. John HS's claim at Beggary Hills in Wedderburn was similar. I was astounded at the lack of punch there too.....as well as the sheer noise!

[Off Grid]

Thanks for these replies, very useful. Like much else, this topic was all done and dusted long before I joined the forum. Being a retro sort and a GB-junkie it looks like I need to add a GB Pro to my collection.

[geof_junk]

I found that the ground I detected ( Vic, Qld & WA ). WA was the worst for hot rocks with a low frequency VLF detector I think Vic Beggary Hills in Wedderburn 1980 with the same detector was less effected by hot rocks but the depth was reduced more than WA. As far as PI detectors were concerned the only problem was salt patches in WA. As far as Qld was concerned the Rangers at the time, the ones I encounter,  put me off nugget hunting and found the beaches were too kind to me, to chase the nuggets instead of gold rings. By the way I have found ground that was worse the Beggary hills for depth, when I was exploring new ground for patches in both WA and Vic..

[phrunt]

When I was a kid in Brisbane, Queensland, Australia my parents house near a Bauxite mine, I used to ride around on my bike there in my early years with my mates, later on we rode dirtbikes around in there, I think it's all filled in and houses now, our dirt was red as red could be, grass even struggled to grow, didn't help by the climate, our gardens were terrible, we had to buy in top soil to grow anything worthwhile as the soil was terrible, the one thing that did grow oddly was Coffee trees, I grew my own beans and roasted them in a popcorn air popper 😉

I didn't care at all about metal detecting then but obviously the soil was pretty hot.  I'm glad I don't have to detect around there now with my mild soil around here.

I would guess there are soils all over the world that can be difficult, we have very mild soil here but absolutely insane hot rocks, a very volcanic country probably doesn't help with that.  

If you look at countries by iron ore production Australia is at the top of the list, I guess that doesn't mean they have the most, it means they mine the most, I have no idea which has the hottest soils, some country somewhere may surprise us all.  Excuse my crazy spacing at the bottom of the post, it won't let me fix it.

1	Australia	930,000	2019
2	Brazil	480,000	2019
3	China	350,000	2019
4	India	210,000	2019
5	Russia	99,000	2019
6	South Africa	77,000	2019
7	Ukraine	62,000	2019
8	Canada	54,000	2019
9	United States	48,000	2019
10	Kazakhstan	43,000	2019
11	Iran	38,000	2019

 

[Norvic]

I concur with AU somewhat but I`ve detected some in NT and a lot in FNQ also, and I`ve found there is as hot as spots in all  States detected in, from DP posts I`ve noted the US has also has hot spots thus assume it is a so for everywhere in the world, I do note "hot ground" near primary deposits but then there are areas that are encroached on by alluvial overburden of a negative "hotness" which are near impossible to work if distributed over surface and at depth over the primary deposits. 

Thus OG, I think to define detecting hot ground by presence of just say iron ores is too narrow a field, I suspect detectors like the Axiom that display a digital value can possibly be set as a standard for such but then detector manufacturers would need to all adopt the same standard for this data to be meaningful. As the Axiom becomes more widespread perhaps DP members could compile an Axiom database that helps data junkies.😉

[Steve Herschbach]

Not to start a pissing match, but I saw nothing in Australia any worse than what I see in the Sierra Mother Lode country, and if anything the issues with dense magnetite soil are worse in the Sierras. There is a place here us locals talk about that to this day the best Minelab machines can barely function in, and so only the largest and shallowest nuggets get found. But yeah, it's an iron mine. The bottom line is geology is local, not a national thing, and localized areas anywhere in the world can be extreme. Bruce Candy himself says that in longer fashion below.

From Bruce Candy at https://www.detectorprospector.com/files/file/52-metal-detector-basics-and-theory/:

"In geologically new soils, the degree of mineralisation is usually weak, except for some volcanic soils. These relatively new soils are commonly found in North America and Europe (from glacier scrapings during the last ice age and mountain erosion etc). In contrast, surface soils which have remained surface soils for a long time often have high mineralisation, because the action of water, over a long period, causes iron compounds to migrate to the surface. For example, Australia has old soils, having had no glaciers recently or significant mountains to be eroded. Some volcanic rocks or sands, known as black sands, may be highly mineralised and are found, for example, in a few USA mainland and Hawaii areas. These black sands (or rocks) are made of mostly magnetite, an iron oxide called ferrite. These typically produce almost entirely X signals, and almost no R. They are heavy, that is they have a high density, and can be identified because they are strongly attracted to a magnet. Small roundish magnetite/maghemite pebbles (a few mm in diameter) are also attracted to a magnet. These, for example, may be found in many Australian goldfields, but do produce significant R signals. Thus, USA goldfields are typically different from Australian goldfields:

• The USA soils are mostly mildly mineralised but in some areas may contain either nearly pure magnetite black sands or rocks, which are problematic for metal detectors as they have very high X components (strongly attracted to magnets).
• Australian goldfields have highly mineralised soils, but very few black sands or rocks that contain nearly pure X magnetite. The magnetic materials are in the forms of magnetite-rich small pebbles and rock coatings, clays and general “sandy” soils. These all contain magnetic materials that produce high levels of X signals as well as R. The ratio of X and R is random, and the R component arises from extremely small magnetic particles called superparamagnetic materials, which are discussed below."

[TE Gold]

7 hours ago, Norvic said:

I concur with AU somewhat but I`ve detected some in NT and a lot in FNQ also, and I`ve found there is as hot as spots in all  States detected in, from DP posts I`ve noted the US has also has hot spots thus assume it is a so for everywhere in the world, I do note "hot ground" near primary deposits but then there are areas that are encroached on by alluvial overburden of a negative "hotness" which are near impossible to work if distributed over surface and at depth over the primary deposits. 

Thus OG, I think to define detecting hot ground by presence of just say iron ores is too narrow a field, I suspect detectors like the Axiom that display a digital value can possibly be set as a standard for such but then detector manufacturers would need to all adopt the same standard for this data to be meaningful. As the Axiom becomes more widespread perhaps DP members could compile an Axiom database that helps data junkies.😉

I live in the NT.

Our ground is very mineralised. 

Uranium,lithium, tantalite and iron ore, along with copper etc...the Iron Ore around Francis Creek area is so pure, that I have seen 2 pieces welded. I tried to find the photo, but sorry can not.

Other parts of the NT are not as bad, but not as rich either.

[Gold Catcher]

18 hours ago, Steve Herschbach said:

18 hours ago, Steve Herschbach said:

There is a place here us locals talk about that to this day the best Minelab machines can barely function in, and so only the largest and shallowest nuggets get found. But yeah, it's an iron mine. The bottom line is geology is local, not a national thing, and localized areas anywhere in the world can be extreme

 

I totally concur with that. Mineralization and hot rocks greatly vary by region, and I don't think that general metrics, that describe entire countries, are an accurate reflection. I have not been to OZ yet, but the worst I have ever seen are in some areas of the Mojave Desert that had extensive volcanic activities (I complain about this a lot here on DP....🤬). The serpentine shist in the Motherload is also not for the faint hearted and some areas there are totally off limits for any detector. One thing to remember is that gold is rarely associated with mild soils. So, here is where I see the most advancements in detector technology opportunities: make them work better in highly mineralized soil and in hot rock infested areas (including deep ones that sound like gold and that you can't simply kick away), without losing sensitivity for small(er) gold. The 6000 was not an improvement in this regard! In fact, it is very hot rock sensitive, does'nt really matter much whether with mono or 14DD. The Axiom seems to perform much better here from what I have read, but the sensitivity to small gold in close vicinity to hot rocks might also be reduced. I doubt that the Axiom has solved this issue once and for all, but I would be glad to be corrected here (I never used one). I think it will take some real revolutionary new technology (not just playing with timings) to convincingly make a difference here. And I count on Bruce Candy for this one!

GC

"While hot rocks can be incredibly annoying, they are actually a good indicator that gold may be nearby. As most experienced prospectors know, the yellow metal likes to hang out in highly mineralized ground. In fact, the worse the soil is and the more hot rocks there are, the better the odds of walking over a nugget."

Hot rocks - Part 2 - Treasure Talk (minelab.com)