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Reno Chris, Please Help Identify Hot Rock


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Chris,

The rocks I found last week with the GB2 that after cleaning with acid I assumed to be ironstones.  Jet black, porus exterior, quartz intrusions, however; I showed them to my son today and they have 0 magnetic pull.  We then gave one a crack with the hammer and wow!  It fractured in dozens of pieces, the inside jet black, shiny cleaved plate like surfaces.  You can see tiny intrusions of quartz and other host rock.  My immediate thought is some type of lead ore, Its very heavy and very metallic to the GB2, but not magnetic.  Your thoughts and anybody else with similar experience. 

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A photo would be of immense help. Does the rock signal with the disc mode on - in other words, does it read as non-ferrous? If you ground balance to the rock, can you get it to ground balance out? If so, what is the ground balance setting?

 

If you can find a piece of white un-glazed porcelain tile (a streak plate) scratch a piece of the rock on it as hard as you can. Does it leave a colored streak? Will a piece of the rock scratch glass?

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Steve,

This website doesn't like photo's with too high resolution.  I'm charging up the old trusty Nikon D70, hopefully, I can jigger the settings around to get a passible photo.  With my little pocket Nikon, the reflective surface of the rock is returning the flash and blowing out the contrast.  Maybe tomorrow I can take one with natural light and get the thing to work.  I left the detector in Yuma, so I can't do much to check the levels you describe.  Imagine a rock nearly as heavy as lead, about the size of a charcoal briquet, weathered with a sliica type coating, an  internal structure of black, shiny flaked crystal, that fractures like glass.  I found 2 of them in the space of 20 ft and quit digging blow out signals.  The area is AZ, within 30 miles of the Cargo Muchacho and Choclate Mountain ranges. 

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Max limit on a single photo upload is 4MB - if photos are larger than that just resize them. The forum will resize all photos to no more than 1024 pixels in the longest dimension anyway. If you resize the photo yourself to no more than a length or width of 1024 pixels it will upload easily.

 

The black, glassy luster and fracturing is what puzzles me. Probably not galena by what you are describing. The only way you get black galena is if it has an extremely high silver content but then it tends to be more sooty looking. Chris will probably chime in soon.

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Pure galena does not register on a detector normally so I am guessing you have galena, lead ore, enriched with silver. Which then makes it silver ore. I have a few high grade specimens I picked up in Arizona with a Gold Bug 2, very heavy, sooty black exterior. I will post a photo when I get a chance. Tombstone, Arizona is famous for its high grade silver ore. Here is a photo of Tombstone ore from http://skywalker.cochise.edu/wellerr/mineral/silver/silver-ore2.htm

 

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Click on photo for larger version

 

This is a good example of stuff that a pulse induction detector will probably miss, but which a hot VLF will signal well on. Not all hot rocks are worthless and in fact you should always make sure you know what they are. An astute prospector might avoid a detector that eliminates hot rocks and instead focus on seeking hot rocks out. I can pretty much promise anyone doing that will eventually find valuable ore minerals. I plan on doing more of that myself, seeking out things other than gold with a metal detector, like silver and copper and platinum.

 

The scary hting is how many meteorites get tossed or ignored as hot rocks!

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