Applied mineral exploration methods, hydrothermal fluids, baro-acoustic decrepitation, CO2 rich fluids
Viewpoints:

How CO2 inclusions form from aqueous fluids

Understanding heterogeneous fluids : why gold is not transported in CO2 fluids

Gold-quartz deposits form from aqueous heterogeneous fluids: NOT from CO2 fluids

Inclusion shapes can prove heterogeneous FI trapping

Disproportional FI trapping from heterogeneous fluids explains gas-dominant systems

A discussion of H2 analysis by mass spectrometry

A mechanism to form H2 in the MS ioniser during analyses


News:

Sangan skarn Fe deposits, Iran

New model 205 decreptiometer

Studies of 6 Pegmatite deposits

A study of the Gejiu tin mine, China


Exploration using palaeo-hydrothermal fluids

Using opaque minerals to understand ore fluids


Understanding baro-acoustic decrepitation.

An introduction to fluid inclusions and mineral exploration applications.



 Interesting Conferences:


AGCC expo, Adelaide, Aust. Oct. 14-18 2018

-----2019-----

ECROFI, June 24-26, Budapest, Hungary

AOGS, Singapore, 28 Jul-2 Aug 2019

SGA, Glasgow Scotland, Aug. 27-30 2019


Comprehensive Geology Conference Calendar


The Arltunga goldfield area, NT, Australia

Conclusions

The gold in this area was transported in and deposited from fluids rich in CO2.  The auriferous quartz formed from these pregnant fluids can be readily identified and distinguished from other barren quartz using the decrepitation method, which is a useful additional exploration tool in this region.


Discussion

The Arltunga goldfield is some 100 Km ENE of Alice Springs, NT, and was discovered in 1887, along with the nearby White Range gold deposits, some 5 Km away and the Winnecke deposits.

20 samples were collected from the Arltunga area from old mullock dumps, and 5 samples were obtained from the White range mine during its operation in 1985.

Gold mineralisation occurs within quartz veins hosted by proterozoic gneisses and schists.

The locations are shown here.  Precise, individual sample location details are not available.

NOTE: the following location map does not work if you are using ie 6 as your browser.  If you only see a map of USA, use firefox >3 instead. It works.



The green marker is Alice Springs town. The red marker is the Arltunga goldfield where 19 samples numbered 330964 to 330983 were collected. The Yellow marker is the White range mine area, from which 5 samples were analysed. The cyan marker is the Winnecke goldfield. No samples have been analysed from there. Click on the coloured pin icons for location details.

These samples 330964 to 330983 were all collected from the old Arltunga workings area, within a radius of about 1 Km from the crossroads.

Sample 330964 was of float from the old mill site and is probably spilled ore. Note the substantial low temperature CO2 decrepitation peak.
arltunga decrep


Samples 330965 - 330967 were from old workings pits beside the road. Again these samples have substantial low temperature decrepitation caused by CO2 rich fluids.

arltunga decrep



Samples 330968-330970 were from old workings east of the road, on a small hill. Only one of these samples (330970, blue) has substantial low temperature CO2 caused decrepitation.
arltunga decrep



Samples 330971-330973 were of quartz collected from a nearby alluvial watershed, unassociated with old workings. They are presumably barren quartz and all of these lack low temperature decrepitation.
arltunga decrep



Samples 330974 & 330975 were from a small pit at the crossroads. They show essentially no decrepitation at all!
arltunga decrep



Samples 330976-330978 were from small workings WNW of the crossroads. These samples do decrepitate above 400 C, but lack any low temperature decrepitation.
arltunga decrep



Sample 330979 was from from quartz outcrop (presumably barren) on a hilltop NW of the crossroads. It has no decrepitation at all.
Samples 330980-330983 were from mullock dumps at old workings on in this same area NW of the crossroads. Three of these samples have low temperature decrepitation indicating the presence of CO2 rich fluids.
arltunga decrep


The White Range mine

Three of the 5 samples from the White ridge mine area have substantial low temperature decrepitation caused by CO2 rich fluids. The other 2 samples have low level decrepitation at low temperatures, indicating traces of CO2 rich fluids.

white range decrep


Summary

No gold analyses on these samples are available. However, based on the proximity to old workings, it is clear that most samples which are probably auriferous also have significant low temperature decrepitation, while most of the barren control samples lacked decrepitation at low temperatures.

It is concluded that the gold in this region is strongly associated with CO2 rich fluids, which are readily detected in the quartz by the decrepitation analyses. There are multiple types of quartz in the area, which cannot be distinguished visually. These  other types of quartz either lack all decrepitation, or only decrepitate at high temperatures above some 400 C. It is probable that these other quartz types are not associated with gold mineralisation, but they can be easily distinguished from potentially auriferous quartz using decrepitation analyses.

Thin sections were made of 7 of the samples to visually examine the fluid inclusions. These observations will be added here.

Conclusions

The gold in this area was transported in and deposited from fluids rich in CO2.  The auriferous quartz formed from these pregnant fluids can be readily identified and distinguished from other barren quartz using the decrepitation method, which is a useful additional exploration tool in this region.

Sample details

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