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


Meguma Terrane, Nova Scotia, 2002

A comparison of gold deposits across eastern Nova Scotia

Kingsley Burlinson,
Burlinson Geochemical Services Pty. Ltd.
Darwin, NT, Australia


Abstract:

In July 2002 a suite of quartz samples was collected from Au deposits and background areas across the Meguma terrane of eastern Nova Scotia for acoustic decrepitation analysis of the fluid inclusions. The results allow comparison between the deposits in this region and assesment of the degree of inhomogeneity within veins and vein sets at these deposits. The results can also be compared with similar data from the Victorian goldfields in Australia which is widely considered to be a similar type of gold occurrence.

Although the presence of gas-rich (CO2) bearing fluid inclusions, as indicated by low temperature decrepitation below 300C,  is common throughout the Meguma of eastern Nova Scotia, it is not in itself a sufficient indicator of Au mineralisation on a regional scale. There is a tendancy for CO2 rich fluids to be found near known batholiths, with some major exceptions such as the Forest Hill mine area. It therefore seems likely that there are both regional metamorphic and batholith related quartz veins in the Meguma, and both of these types of quartz can be auriferous. Decrepitation patterns within individual districts or mines can be useful in distinguishing the different quartz events, as seen in the Beaver Dam and Dufferin mines. But in other cases, such as Wine Harbour, different vein orientations are indistinguishable and suggest that structural orientation of the veins is not a sufficient indicator of a different hydrothermal origin of the quartz.
 

Methods:

Because none of the mines was operational and some had been reclaimed, samples were usually collected from mine dumps and their exact original  location is indeterminate. To compensate for this, many samples were collected which allows an assessment of inhomogeneity of the quartz and discrimination between superimposed quartz veins of different origins. The samples were analysed in the Burlinson Geochemical Services model 105 decrepitometer (Burlinson, K. 1988).To facilitate comparison of the gas (predominantly CO2) component of the inclusions, the results have been plotted on a non-linear  y-axis scale which suppresses the effect of background interference counts below about 10, accentuates the range of counts from 10 to 1000, and suppresses counts above 5000. This has the effect of highlighting the important data between 150 and 300 C, which is the range of decrepitation temperatures of gas rich CO2 inclusions.
 

References

Linear plots of this same data

Microscope observations of 11 selected samples

sample location map, eastern Nova Scotia.

These samples were from a roadside gravel quarry, not expected to be auriferous. But the result shows a moderate amount of decrepitation below 300 due to gas rich inclusions and shows similarity with auriferous quartz. The other 2 unmineralized background locations at Sonora and Moser river lack this low temperature decrepitation. Note that the musquodoboit quarry sample is very close to a batholith contact.  The low temperature decrepitation here is a function of the nearby intrusion which has supplied gas rich, high pressure fluids.

Musquodoboit background sample description. Map location "MUSQ"



 

Samples from the Mex pit west end (above) have only minor levels of low temperature decrepitation, in marked contrast to samples from the central zone of this pit (below). This mine is near an outcropping batholith. This decrepitation variation over a short distance within the pit may well be reflecting the Au gold grade variations.

Beaver Dam sample descriptions. Map location "BEAVD"
 
 


The very high levels of low temperature decrepitation in all the samples from 15 mile indicate very gas rich inclusions. Although this mine is some 5 Km from an outcropping batholith there may be a closer, non-outcropping batholith, or a good fluid pathway from the nearby outcropping batholith.

15 Mile sample descriptions. Map location "15MILE"



 

The Dufferin mine was closed when visited, so samples were collected from 2 separate dumps, said to be of upper or lower saddle reef quartz. There is no clear distinction between the 2 saddles, but 3 of 5 samples from the upper saddle show a pronounced decrepitation drop near 550 C, and none from the lower saddle show this feature. This might be indicating a difference between the saddles if 2 of the dump samples from the upper reef are actually contamination on the dumps from the lower reef. Low temperature decrepitation occurs on only 2 of these 10 samples, and 2 previous samples also lacked low temperature decrepitation. Although there are some samples with abundant gas rich inclusions at this mine, their relationship to the Au mineralisation cannot be deduced from these limited samples. There seem to be 3 distinct types of quartz recognizable.

Previous analyses of well located quartz from a limb and a nose of a reef at Dufferin did show a recognizable difference between the two sites, but more than 2 samples is necessary to confirm this tentative conclusion.

Dufferin Mine sample descriptions. Map location "DUFF"

Samples 2008B (green above) and  2008C (blue above)  were examined microscopically to check the presence and absence of CO2 rich inclusions. Sample 200D (cyan above) was also examined to check why it had such low decrepitation intensity.
 
 

Samples 2009D (magenta above) and 2009E (blue above)  were examined microscopically to understand why they differ so much in decrepitation intensity near 550 C.
 



 

The Goldenville mine is near a batholith outcrop, although separated from it by a major fault. None of the 12 samples has intense low temperature decrepitation, but 4 of them show significant low temperature decrepitation, with minor amounts in the other samples. Where it was possible to identify crosscutting veins, these tend to have lesser low temperature decrepitation and are quite similar to the nearby Sonora background samples (below). However this differentiation is tenuous as the other samples show only marginally more intense decrepitation at best. There is a weak suggestion of a relationship between gas rich inclusion content and Au mineralisation in these results.

Goldenville sample descriptions. Map location "GOLDV"


 
 

Goldenville sample descriptions. Map location "GOLDV"



 

The  Sonora Rd. background sample lacks significant low temperature decrepitation and has low gas content inclusions only. This is similar to the Moser river background samples, despite the Sonora samples being very close to a batholith contact. I interpret that these veins were related to a regional event rather than to the batholith intrusion, as the latter would have given gas rich inclusions as seen in the Musquodoboit background.

Sonora Rd. background sample descriptions. Map location "SONORA"



 

The Wine Harbour samples all have negligible low temperature decrepitation and little if any gas rich inclusions.
Decrepitation data alone could not be used to discern if these veins were auriferous. In fact, the samples are all remarkably self similar suggesting a very homogenous origin for both the bedding parallel and crosscutting veins. The multiple samples from individual veins also confirm that quartz within individual veins is homogenous. These veins must have been deposited from an invariant hydrothermal system - perhaps a metamorphic system rather than batholith driven?

Wine Harbour sample descriptions. Map location "WINEH"


 
 

Wine Harbour sample descriptions. Map location "WINEH"



 

Despite being near an outcropping batholith, very few of the Cochrane mine samples (only 3 of 24) show low temperature decrepitation. However all but one sample show a major drop in decrepitation intensity near 550 C. This characteristic is only seen elsewhere on some of the Dufferin samples and most of the Forest Hill samples. Despite sampling various areas of the pit, most samples are similar, with only 2 samples from the central are of the pit being significantly different and containing moderate amounts of gas rich inclusions.

Cochrane Hill pit sample descriptions. Map location "COCHR"

Sample 2017C (blue above) was examined microscopically and compared with Upper Seal harbour and Forest Hill samples to understand the decrepitation decrease near 540 C.
 


 
 

Cochrane Hill pit sample descriptions. Map location "COCHR"


 
 

Cochrane Hill pit sample descriptions. Map location "COCHR"


 
 

Cochrane Hill pit sample descriptions. Map location "COCHR"


The Skunk's Den mine samples are all quite similar, with only 2 bedding parallel samples from the south fold limb showing some low temperature decrepitation from gas rich inclusions. The sampling of different vein sets did not reveal them to be of different origins. A number of samples show a pronounced decrepitation peak near 530 C but it is unclear what this is related to. The lack of gas rich inclusions is consistent with the absence of nearby batholiths.

Skunk's Den Mine, Sable road cutting, sample descriptions. Map location "SKUNKS"


 
 

Skunk's Den Mine, Sable road cutting, sample descriptions. Map location "SKUNKS"


 
 

Skunk's Den Mine, Sable road cutting, sample descriptions. Map location "SKUNKS"


The 2 separate types of quartz collected here gave no discernible decrepitation difference. Unlike the nearby Skunk's Den mine, moderate intensity low temperature decrepitation occurs on over half of the samples at Upper Seal harbour although there are no nearby batholiths. Several of the samples also show prominent decrepitation near 530 C, similar to many of the Skunk's Den mine.

Upper Seal Harbour mine sample descriptions. Map location "SEAL"

Samples 2019C (blue above) and 2019E ( magenta above) were examined microscopically and compared  to confirm the CO2 rich inclusions causing the low temperature decrepitation in sample 2019C.


 

Sample 2020B (green above) was examined microscopically and compared with Cochrane Hill and Forest Hill samples to understand the lack of decrepitation decrease near 540 C.
 


Samples from Isaac's Harbour all show very low or no low temperature decrepitation and lack gas rich inclusions. There is a suggestion that there are 2 types of quartz here, based on the amount of decrepitation up to 300 C.

Isaac's Harbour mine sample descriptions. Map location "ISAAC"

Isaac's Harbour carbonate samples (3)


Forest Hill samples show a complete absence of low temperature decrepitation, despite the presence of nearby batholiths. In addition, the overall decrepitation intensity on all these samples is quite low. Many samples, including all those from the Teasdale shaft area, show a pronounced decrease in decrepitation at 550 C - a feature peculiar to Cochrane hill and a few Dufferin mine samples.  Although it was very difficult to sample this completely reclaimed deposit, the lack of low temperature decrepitation in all of these 15 samples is probably a real feature of the deposit rather than a sampling aberration.

Forest Hill  mine, 900E zone sample descriptions. Map location "FORES1"

Forest Hill mine, teasdale shaft area sample descriptions. Map location "FORES2"

Sample 2023F (brown above) was examined microscopically and compared with Cochrane Hill and Upper Seal harbour samples to understand the decrepitation decrease near 540 C.


This background sample is remote from any batholith and has negligible low temperature decrepitation, inferring negligible gas rich inclusions. I consider this quartz to be a separate event to the granite related quartz.

Moser River area, on NS route 7,  background sample descriptions. Map location "RTE7NS"


Sample location map, eastern Nova Scotia.

Microscope observations of 11 selected samples

In 1999, a group of samples were collected from old diggings near the coatline at the Ovens deposit.  These samples were not collected from the well known coastal outcrops and may not be entirely representative of this deposit

A suite of samples has been collected from the Black Bull silica deposit in western NS. These samples all had remarkably identical decrepigrams, suggesting an unuasually homogenous single emplacement event.

Samples were collected from the East Kemptville (polymetallic, Sn) (Mt. Pleasant) deposit in 1999.  At this date the mine was closed and being reclaimed so samples were from dumps, with a few from accessible pit faces.

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