Bauxite.....gold found in similar ground?
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shakergt
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I am no Geo but I do know that Alcoa mine Bauxite very close to the gold mine in Boddington.
i dont know that gold & bauxite are specifically connected, but the mineralology in some areas may produce both.
Here in the S/W of WA we have a BIG goldmine smack bang in the middle of a huge bauxite area (Worsley Alumina - South32, & ALCOA)
Newmonts Boddington Gold Mine.
Here in the S/W of WA we have a BIG goldmine smack bang in the middle of a huge bauxite area (Worsley Alumina - South32, & ALCOA)
Newmonts Boddington Gold Mine.
Boddington used to be a bauxite as well as a gold mine, with gold even in the bauxite. However the process that produces bauxite only has a secondary relationship to that which produces gold - the presence of bauxite is not a direct indicator of gold. Bauxite is simply a special type of soil rich in aluminium, formed by extreme weathering - so bauxite can form from many rock types. The bauxite at Gove has formed from sedimentary rocks of Mesozoic age, and rocks of this age are not known to contain gold deposits in that region - personally I would not consider it prospective.
Because bauxite can formed from many rocks, in places like Eastern Australia and southwest WA bauxite has instead formed from mafic igneous rocks, such as Tertiary basalt or Archaean metabasalt, respectively. Since these rocks can also contain gold in WA, gold and bauxite can occur together in WA. The process is slightly more closely related than that, in that gold from the unweathered metabasalt at depth can be dissolved and re-distributed at surface in the weathering zone, often in the form of nuggets (so gold derived by dissolving gold from primary deposits at depth can crystallize in the bauxite soil at surface, and those spherical bauxite pisolites are sometimes found completely enclosed in the gold nuggets). But the gold will only be there if there is gold at depth, the bauxite can form there and throughout the surrounding region (e.g. along the Darling scarp in WA). So asking if bauxite can contain gold is like asking if soil can contain gold it depends what rock the soil has formed on. HOWEVER, bauxite increases the chance of nuggety gold when gold is present.
How does bauxite form? As the basalt (in WA and Victoria anyway) weathers, its iron, magnesium, calcium and sodium and minor potassium minerals first form clays called smectites (hydrated sodium and calcium aluminium silicates such as montmorillonite - swelling clays) with some illite (hydrous potassium aluminium silicate clay). They are hydrous minerals because they have had rain water added to the rocks in the weathering zone. These weather further and the iron and calcium are weathered out of the clays, leaving the illite and hydrous aluminium silicate (kaolinite clay) if the potassium is also removed. If weathering is very intense, the rock will become a pure white kaolinite, often called saprolite (this can have an iron capping or nodules overlying or within it - ferricrete, formed from the iron that has been leached out of the original rock and re-deposited as hydrous iron oxides - goethite, limonite). Sometimes this soil profile of early clays, white saprolite, and black ferricrete is collectively referred to as laterite.
In a minority of cases the weathering goes even further and the silicon is removed from the kaolinite, so all that is left is hydrous aluminium oxide minerals (gibbsite, boehmite and diaspore) - which comprise the ore we call bauxite, the ore of the metal aluminium.
Because bauxite can formed from many rocks, in places like Eastern Australia and southwest WA bauxite has instead formed from mafic igneous rocks, such as Tertiary basalt or Archaean metabasalt, respectively. Since these rocks can also contain gold in WA, gold and bauxite can occur together in WA. The process is slightly more closely related than that, in that gold from the unweathered metabasalt at depth can be dissolved and re-distributed at surface in the weathering zone, often in the form of nuggets (so gold derived by dissolving gold from primary deposits at depth can crystallize in the bauxite soil at surface, and those spherical bauxite pisolites are sometimes found completely enclosed in the gold nuggets). But the gold will only be there if there is gold at depth, the bauxite can form there and throughout the surrounding region (e.g. along the Darling scarp in WA). So asking if bauxite can contain gold is like asking if soil can contain gold it depends what rock the soil has formed on. HOWEVER, bauxite increases the chance of nuggety gold when gold is present.
How does bauxite form? As the basalt (in WA and Victoria anyway) weathers, its iron, magnesium, calcium and sodium and minor potassium minerals first form clays called smectites (hydrated sodium and calcium aluminium silicates such as montmorillonite - swelling clays) with some illite (hydrous potassium aluminium silicate clay). They are hydrous minerals because they have had rain water added to the rocks in the weathering zone. These weather further and the iron and calcium are weathered out of the clays, leaving the illite and hydrous aluminium silicate (kaolinite clay) if the potassium is also removed. If weathering is very intense, the rock will become a pure white kaolinite, often called saprolite (this can have an iron capping or nodules overlying or within it - ferricrete, formed from the iron that has been leached out of the original rock and re-deposited as hydrous iron oxides - goethite, limonite). Sometimes this soil profile of early clays, white saprolite, and black ferricrete is collectively referred to as laterite.
In a minority of cases the weathering goes even further and the silicon is removed from the kaolinite, so all that is left is hydrous aluminium oxide minerals (gibbsite, boehmite and diaspore) - which comprise the ore we call bauxite, the ore of the metal aluminium.
DD, Davent,
Worked for Alcoa for 31 years, during that time there were various experiments to extract other valuable minerals. These experiments at Pinjarra failed.
The gold mined at Boddington is microscopic, you won't find any there with your metal detector.
Having said that, who knows in the years ahead a process maybe developed to retreat the massive dumps that have piled up in the 60+ years of bauxite/alumina production.
Remember when the claim was made that Kalgoorlie Streets were paved with gold.
http://museum.wa.gov.au/explore/wa-goldfields/rush-gold/streets-paved-gold
The Carbon in Pulp process was born.
https://www.911metallurgist.com/blog/gold-cil-process-explained
Worked for Alcoa for 31 years, during that time there were various experiments to extract other valuable minerals. These experiments at Pinjarra failed.
The gold mined at Boddington is microscopic, you won't find any there with your metal detector.
Having said that, who knows in the years ahead a process maybe developed to retreat the massive dumps that have piled up in the 60+ years of bauxite/alumina production.
Remember when the claim was made that Kalgoorlie Streets were paved with gold.
http://museum.wa.gov.au/explore/wa-goldfields/rush-gold/streets-paved-gold
The Carbon in Pulp process was born.
https://www.911metallurgist.com/blog/gold-cil-process-explained
Boddington is a bit different and lacks nuggets as you say, but my comments are valid in general for WA- Boddington is a gold-copper mine and this may have influenced grain size. The mine produces 850,000 ounces of gold and 30,000 tonnes of copper per year and will achieve this rate for the next 20 years, so it is rather different to other mines in the goldfields. However it has long been mining deeper ore (initially the ore was all laterite), and I don't know the grain size near surface (it is 1 to 10 micron elsewhere, locked inside sulphide minerals). Precipitation of secondary gold in laterites usually involves reduction on the iron-rich ferricrete (so common that some people refer to "ferricrete gold deposits"). However secondary copper minerals could be expected to occur in the weathering zone at Boddington and gold may occur with that - I have not read any mineralogical reports on the upper ore (although I know some gold in the upper zone is in cutans and pisolite rims).Nightjar said:
However the coarse gold - ferricrete relationship is common throughout the eastern goldfields at least (photos) - weathering rarely goes all the way to bauxite ore although some gibbsite, diaspore etc is commonly present with the gold.
