Dome mine, Ontario

Dome pit decrepitation sample results

Timmins, Ontario

In May 2000, 17 samples were collected from the Dome pit at Timmins. These were of quartz veins from the pit walls on the west and north sides of the pit and the samples were analysed by fluid inclusion decrepitation to ascertain if this method would assist with exploration and mine development .

Samples 1933 to 1936 were collected from the west and north-west wall of the pit on the 5735 bench below thepit observation area. Sample1937 was collected to the north from the North Syncline area. Sample 1938 was collected further north again from slate hosted veins. Sample 1939 was of quartz from the Dome fault. Where possible, multiple samples were collected from each site within a 5 metre radius and these were assigned suffixes of the same sample number. By analysining these suffixed samples independantly we get an idea of small scale inhomogeneity of the results to compare with the larger pit scale variations seen between different sample numbers.

There are 3 distinct types of response pattern in the samples analysed, which distinguish seperate quartz vein parageneses.

Samples with a prominent low temperature peak indicative of very high CO₂ content in the inclusions. These samples also have high intensity decrepitation in the 500^oC region. This is seen in samples 1933 to 1937.
Samples with moderately intense decrepitation in the 500^oC region, but which lack low temperature decrepitation and have little or no CO₂ content in the inclusions. This occurs in sample 1938.
Samples with weak decrepitaion in the 500^oC region and also lacking low temperature CO₂caused decrepitation. This is seen in sample 1939.

In general, CO₂rich fluid inclusions are closely associated with Au mineralisation and this has been documented in the Timmins district. In these samples, the high CO₂ samples are in the west and north-west areas of the pit. My recollection is that these were the lower Au grade areas. The north wall areas (slate hosted, sample 1938) lack CO₂rich inclusions, but show moderate intensity decrepitation in the 500^oC temperature region. My recollection is that this area was actually of higher Au grade. The samples from the Dome fault (1939) lacked CO₂ inclusions and also had very low intensity decrepitation in the 500^oC region.

There are some variations in other features of the decrepigrams, which cannot be reliably interpreted on this small suite of samples, but which may be relevant on a larger sample suite. In particular, the peak near 500-550^oC on most samples occurs at markedly lower temperature at 460^oC on samples 1933A and 1936.

Variations between samples collected at the same physical site (same number but different suffices) show the degree of local inhomogeneity. To reliably seperate quartz generations, variations between quartz types need to be greater than this observed small scale variability.

Summary

At the Dome mine, there are major variations in the quartz decrepitation patterns across the pit. The results show that quartz in some areas contains abundant fluid inclsions with high partial pressures of CO₂, whereas nearby, visually similar quartz can be quite different with low inclusiion abundance and no CO₂ rich inclusions. This has potential as an exploration guide, particularly in drill samples where quartz vein relationships are less obvious than in the pit walls. Quartz samples from the Dome fault have a distinct decrepigram pattern that can be used to identify and distinguish this generation of quartz emplacement . Additional variations are present in the data and may be interpretable and of exploration significance on a more extensive sample suite with more thorough sample location and Au analytical control than was possible during this quick orientation study.

The Data:

H1213 Sample# 1933A Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, west wall below lookout
Milky wh massive qtz vein with ankerite

H1214 Sample# 1933B Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, west wall below lookout
Milky wh qtz Carbonate and grey siliceous CR

H1215 Sample# 1934 Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, west wall, 100m north of 1933
massive milky wh qtz, vitreous lustre

H1216 Sample# 1935 Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, west wall, near 1934, conformable vein
massive milky wh qtz, dull lustre

H1217 Sample# 1936 Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, west wall, 200m further north
massive milky wh qtz, greyish vitreous lustre

The 3 sub-samples of 1937 at this location all show CO2-rich fluids, but also substantial differences from 450 to 550 C, indicating a high degree of small scale variability in the quartz from multiple overlapping parageneses.

H1218 Sample# 1937A Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north syncline conglomerate area
milky greyish white qz, vitreous lustre

H1219 Sample# 1937B Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north syncline conglomerate area
milky greyish white qz, vitreous lustre

H1220 Sample# 1937C Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north syncline conglomerate area
milky greyish white qz, vitreous lustre

Note the absence of low temperature CO₂ decrepitation in all 6 of the samples from this location, sample 1938A to F.

H1221 Sample# 1938A Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, vitreous lustre

H1222 Sample# 1938B Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, vitreous lustre

H1223 Sample# 1938C Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, vitreous lustre

H1224 Sample# 1938D Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, vitreous lustre

H1225 Sample# 1938E Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, vitreous lustre

H1226 Sample# 1938F Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, slate host
milky greyish white qz, dull lustre

Samples from the Dome Fault all show remarkably low decrepitation intensity, as well as the absence of CO₂-rich fluids.

H1227 Sample# 1939A Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, in Dome fault
semi transl greyish-white qtz with ankerite

H1228 Sample# 1939B Can2000 0.5g -420+200u
Timmins, Dome mine pit, 5735 bench, north-east wall, in Dome fault
massive pale gy qtz, chlorite slickensides

H1229 Sample# 1939C Can2000 0.5g -420+200u Acid Washed
Timmins, Dome mine pit, 5735 bench, north-east wall, in Dome fault
semi translucent pale gy qtz

Back to Main Contents