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:

Kalgoorlie Au data

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:

-----2019-----

ECROFI, June 24-26, Budapest, Hungary

AOGS, Singapore, 28 Jul-2 Aug 2019

SGA, Glasgow Scotland, Aug. 27-30 2019

SEG, Santiago Chile, Oct 7-10 2019


Comprehensive Geology Conference Calendar


Decrepitation data of gold deposits in the Kalgoorlie area, Western Australia

In 1994 an extensive suite of samples was collected from several gold deposits in and near to Kalgoorlie

Summary

It is well known that Au mineralization is frequently associated with CO2 rich fluids. Such fluids produce distinctive decrepitation graphs with significant decrepitation at low temperatures, below 300 C, particularly for epithermal type deposits, such as those in the Kalgoorlie region of West Australia. This extensive decrepitation study aimed to document the distribution of such CO2 rich fluid systems and their relationship to gold mineralization..

Many of the samples in the study show evidence of CO2 rich fluids, particularly at the Mt Pleasant and Kalgoorlie superpit areas. In fact samples from these two areas (and the Victory mine at Kambalda) had the most intense low temperature decrepitation of all the samples in my entire database of more then 5000 samples. However there are also areas in which CO2 rich fluids are absence despite known mineralization, such as the Bayley's mine at Coolgardie.

It is also notable that close groups of samples ( those with the same sample number with alphabetic suffixes, collected within a radius of a few metres maximum) can show great variation in low-temperature decrepitation intensity and thus CO2 content. It is clear that quartz veins are quite inhomogeneous, which is not apparent in hand specimen and can only be determined by study of their fluid inclusion populations.

Although low-temperature decrepitation, indicating the presence of CO2 rich fluids,  can be used as a guide to gold mineralization , each deposit and region needs to be assessed individually to confirm the relationship and the degree of local heterogeneity within the quartz veins.


This data is grouped  into seperate areas

Discussion of the Kalgoorlie and Coolgardie areas follows below.

        Brief sample descriptions of the Kalgoorlie area samples are here.

        Brief sample descriptions of the Coolgardie area samples are here.

Discussion of  the Victory mine, near Kambalda (point 3 on this map) is here

Discussion of  the Southern Cross area is here

Discussion of  the Londonderry pegmatite (non-gold) is  here

In all cases same-numbered samples with alphabetic suffixes were collected from the same location within a few metres and show the local variability of the data.

The maps herein are from the Geological Society of Australia (WA division) Excursion guidebook 8 by W.K. Witt, D.I. Groves & S.E. Ho  1994. This document contains extensive geological details of the region and mines visited.

Regional location map

Samples were collected from locations   1,2,3,4 & 5 (numbers inside black circles)  on the following map of the kalgoorlie region

sample location map, kalgoorlie, 1994


Kanowna Belle


Kanowna belle location map


At Kanowna Belle low temperature decrepitation occurs in the ore zone, but some 20m away  (sample 1504) there is only weak low-temperature decrepitation, perhaps reflecting distance from mineralization.

Kanowna belle 1501

kanowna Belle 1502

kanowna Belle 1503

Sample 1504 is some distance from the main ore zone and shows only weak low-temperature decrepitation
Kanowna Belle 1504

Mt Pleasant

The 3 pink shaded deposits were sampled in this study.

Mt Pleasant location map


Sample 1505 has some of the most intense low temperature decrepitation ever observed. However this quartz was waste rock on the coreshed floor and it is uncertain if it was gold mineralized.

Mt Pleasant 1505


Mt Pleasant - royal standard pit 1507

Sample 1508 of breccia contained feldspar which caused the high counts above 600 C. Quartz does not decrepitate above the alpha beta transition temperature of 573 C.
Mt Pleasant - Ratetrack pit 1508
Mt Pleasant - Golden kilometre pit 1509

Kalgoorlie Superpit


Samples from the Kalgoorlie superpit ore zone often show very intense low-temperature decrepitation due to CO2 rich fluid inclusions.
Kalgoorlie superpit 1538
Kalgoorlie superpit 1538
Kalgoorlie superpit 1539
Kalgoorlie superpit 1540
Kalgoorlie superpit 1541
Kalgoorlie superpit 1542
Kalgoorlie superpit 1543
Kalgoorlie superpit 1544

Coolgardie

The 3 mines shaded pink were sampled in this study. The Londonderry pegmatite was also sampled and is reported upon separately here.


Coolgardie map


Unmineralized granite hosted quartz veins

Note the lack of low-temperature decrepitation on these unmineralized quartz samples.

Unmineralized coolgardie area 1510

Unmineralized coolgardie area


Bayley's mine

Only a few of the samples from Bayley's mine show low-temperature decrepitation.  Such decrepitation cannot be assumed to be necessary for gold mineralization on a regional scale.

Bayley's 1523
Bayley's 1524
Bayley's 1525
Bayley's 1526
Bayley's 1527
Bayley's 1528
Bayley's 1529
Bayley's 1530
Bayley's 1531
Bayley's 1532
Bayley's 1533
Bayley's 1534


King's Cross mine

Samples from the King's Cross mine show no low temperature decrepitation.

King's Cross mine 1535

King's Cross mine 1536
King's Cross mine 1537

Three Mile Hill mine

The three mile hill mine is only about 3 Km from Bayley's and King's Cross mines, but has very different fluid inclusion character with intense low-temperature decrepitation.

Three Mile mine 1545

Three Mile mine 1546
Three Mile mine 1547
Three Mile mine 1547
Three Mile mine 1548
Three Mile mine 1549