Report on a Diamond Drilling Program, North River, Victoria County, Nova Scotia
by G. J. DeMont gjdemont@gov.ns.ca
Nova Scotia Department of Natural Resources
Mineral Resources Branch
Open File Report 97-005
Table of Contents
Abstract
A copper occurrence exposed in a large outcrop of Indian Brook Granodiorite along North Brook, Victoria County was evaluated in a 1994 Nova Scotia Department of Natural Resources mineral inventory study. The mineralized outcrop, which is exposed over a 70 m long by 10-15 m wide area in the bed of North Brook, contains a series of parallel, mineralized fractures, with a 3-10 cm wide spacing. Pyrite is the principal mineral developed along the fractures, with lesser amounts of chalcopyrite, bornite, epidote, chlorite, carbonate and quartz. Analyses of mineralized samples of the granodiorite returned values up to 630 ppm Cu and 61 ppb Au.
The mineralized granodiorite outcrop is exposed near an intrusive contact between Indian Brook granodiorite and Murray Mountain quartz monzodiorite. Preliminary results of the mineral inventory examination suggested that the mineralization might be related to the intrusion of the quartz monzodiorite into the granodiorite, and that this might be a favourable area for the development of a large tonnage-low grade style copper-gold deposit.
Three holes were drilled by the Nova Scotia Department of Natural Resources in 1995 to evaluate the Cu-Au potential of this occurrence. Unfortunately, only one of the holes (NBK95-1) reached outcrop because of unforseen drilling problems caused by thick and unstable overburden in the North Brook valley. This hole intersected a weakly mineralized granodiorite which was cut by several diabase and leucogranite dykes.
The down-dip extension of the mineralized outcrop exposed in the brook proved to be less mineralized at depth. However, the leucogranite dykes intersected in this drillhole contain trace amounts of disseminated pyrite, chalcopyrite, hematite and possibly molybdenite. It is possible that these mineralized leucogranite dykes are related to the St. Anns leucogranite, which is known to host, or is spatially related to, several other Cu-Mo±Au occurrences exposed nearby in the St. Anns area. Further studies are required to confirm this hypothesis.
Acknowledgments
I thank E. Standing and G. MacLeod for their hard work in completing drillhole NBK95-1, and for their valiant efforts to drill holes NBK95-2 and NBK95-3.
Introduction
A large outcrop area of mineralized granodiorite exposed along North Brook, Victoria County, was sampled during a 1994 Department of Natural Resources, mineral inventory survey of Central Cape Breton. Analyses of the rock samples collected from this zone returned values up to 630 ppm Cu and 61 ppb Au.
The mineralized zone is located near a contact between Indian Brook granodiorite and Murray Mountain quartz monzodiorite. A preliminary interpretation of the mineral inventory examination indicated that the mineralization may have developed as a result of the intrusion of the quartz monzodiorite into the granodiorite. The large areal extent of the mineralized zone, and the presence of trace amounts of Au, suggests that a granite-related, low grade-high tonnage style, Cu-Au deposit might be found along this contact. Therefore, a three hole diamond-drilling program was undertaken in 1995 to evaluate the mineral potential of this contact zone.
Previous Work
This occurrence was first reported by Brubec Mines (Riddell et al., 1968) in 1968. It was also described briefly in a 1984, Billiton Canada Ltd. assessment report (Dickie, 1984). However, the occurrence was only given a superficial evaluation in both of these regional surveys.
Geology
The mineral occurrence is hosted by the Late Hadrynian-Cambrian, Indian Brook Granodiorite. This is a subunit of the St. Anns-Wreck Cove plutonic suite defined by Barr et al. (1985) as follows:
"The eastern part of the map area is divided into (inferred intrusive sequence from oldest to youngest) Birch Plain Granite, Indian Brook Granodiorite, St. Anns Leucogranite, and Murray Mountain Quartz Monzodiorite. The intrusive sequence is based primarily on observations of granitoid xenolithic material. The Late Hadrynian to Early Cambrian age is based on an Rb-Sr whole rock isochron age of 517±10 Ma for the St. Anns Leucogranite reported by Cormier (1979). The isochron also included one sample of the Indian Brook Granodiorite, which is presumably similar in age but somewhat older. Overall similarity of these units to Late Hadrynian granitoid rocks to the south of St. Anns Harbour supports the age interpretation. Near its western margin the Indian Brook Granodiorite contains abundant xenoliths of the adjacent Barachois River Gneiss, an indication of a late Hadrynian or older age for the latter unit.
The Birch Plain Granite is medium grained, pink to red, with less than about 10% mafic minerals. It consists of microcline, plagioclase (oligoclase), quartz and biotite. Locally the granite is porphyritic, with microcline phenocrysts up to 3-4 cm in length. Amphibole is characteristically absent. Abundant large subhedral grains of sphene are a prominent feature, and other accessory minerals (zircon, allanite) are common. The rocks are variably foliated and deformed. Sericite, epidote and chlorite are abundant secondary minerals.
The Indian Brook Granodiorite is also medium grained and pink to red, but contains 10-30% mafic minerals. It varies in both potassium feldspar and mafic mineral content, and is locally a granite. However, it differs from the Birch Plain Granite in the characteristic presence of hornblende, which is typically more abundant than biotite. Foliation, deformation, alteration, and accessory minerals are similar to those in the Birch Plain Granite.
The St. Anns' Leucogranite is a distinctive medium- to coarse-grained pink rock containing only 1 or 2% mafic minerals (chloritized biotite). Essential minerals are plagioclase (albite-oligoclase), orthoclase (?) perthite, and quartz. Locally aplitic bodies are present within the leucogranite.
The Murray Mountain Quartz Monzodiorite forms the central part of the Murray Mountain peninsula and was largely mapped as hornblende granodiorite, quartz monzodiorite, quartz diorite, tonalite, and their altered equivalents by Barr et al. (1982). This reflects the variation in quartz and alkali feldspar content of the unit, which differs from the previously described units in its more mafic character. It appears to be the youngest unit, intruding both the Birch Plain Granite and the Indian Brook Granodiorite, but an upper age limit is not defined."
The mineral occurrence is located near a mapped contact (Barr et al., 1992) between Indian Brook Granodiorite and Murray Mountain Quartz Monzodiorite, but the actual contact is not exposed. The quartz monzodiorite unit forms a distinct magnetic low which is visible on the vertical gradient magnetic map (Geological Survey of Canada, 1992) of the St. Anns area. A magnetic low also defines the St. Anns Leucogranite and the Murray Mountain Granodiorite which host a porphyry style Cu-Mo showing located on Murray Mountain, approximately 8.5 km southwest of the North Brook occurrence.
Mineralization
The mineralized granodiorite is exposed in outcrop along North Brook for a minimum length of 70 m and a width of 10-15 m. The best exposure is found at the base of a small waterfall located approximately 1100 m north of the junction of North Brook and the Barachois River, and 80 m south of the junction of North Brook and the woods road extension of the Tarbotvale Road.
The granodiorite exposed in outcrop below the falls is cut by mineralized fractures every 3-10 cm, over a 30 m long by 10-15 m wide area. These fractures, which have an approximate strike of 159° Az. and dip 75° SW, are coated in a weak, yellowish- brown limonite stain, making them readily apparent. Pyrite is the principal mineral developed along the fractures, with lesser amounts of chalcopyrite, bornite, epidote, chlorite, carbonate and quartz.
Several other joint sets are present in the outcrop, but these do not appear to be mineralized. Several green diabase dykes intrude the granodiorite in the mineralized outcrop and at least one 80 cm wide dyke parallels the mineralized fractures.
The ferromagnesian minerals in the granodiorite are wholly or partially altered to chlorite and epidote, the plagioclase crystals are weakly to moderately altered to sericite and saussurite, and the K-feldspars exhibit a weak to moderate argillic alteration, which in thin section, imparts a clouded appearance. The granodiorite is also cut by sporadic, thin, <1 mm epidote veinlets.
Diamond-Drilling Results
Diamond-drillhole NBK95-1 was drilled approximately 10 m south of the woods road extension of the Tarbotvale Road, to a depth of 87.5 m, on a bearing of 030° Az. and a dip of -45°. It was drilled to test the down dip extension of the mineralized zone exposed in outcrop in North Brook. The drillhole passed through a weakly mineralized zone in the granodiorite which is assumed to represent the same zone as that exposed in outcrop. However, the frequency of mineralized veinlets present in the drill core is much lower than that in the outcrop exposure. Notwithstanding this, several weakly mineralized leucogranite dykes intersected in the drillhole may represent apophyses of a larger, unexposed, mineralized intrusion.
Drillholes NBK95-2 and NBK95-3 were drilled northwest (see Fig. 2) of drillhole NBK95-1 to test the mapped contact zone between the Indian Brook Granodiorite and the Murray Mountain Quartz Monzodiorite. Unfortunately, both of these drillholes failed to reach bedrock because of a thick and unstable surficial deposit of boulders and sand which caused insurmountable drilling problems.
Conclusions
The drilling program did not intersect any significant amount of mineralization, but the weakly mineralized leucogranite dikes intersected in diamond drillhole NBK95-1 may represent apophyses a larger, unexposed, mineralized intrusion. These dikes contain trace amounts of disseminated pyrite, hematite, chalcopyrite and possibly molybdenite. An analysis of a sample of one 0.4 m thick leucogranite dike intersected in diamond-drillhole NBK95-1, returned values of 65 ppm Cu, <10 ppm Mo and 21 ppb Au.
The mineralized dikes may be related to an unexposed body of the St. Anns Leucogranite, which is exposed on Murray Mountain, and either hosts or is spatially related to significant Cu±Mo±Au occurrences exposed at four locations in the St. Anns area (see mineral occurrence records K07-033, K07-053, K07-054 and K07-055). The St Anns Leucogranite is illustrated by a magnetic low on the airborne vertical gradient map (Geological Survey of Canada, 1992) covering this area. This magnetic low underlies a more extensive area than that defined by the leucogranite geological boundary illustrated on the geological map (Barr et al., 1992), and extends into the site of the North Brook drilling. This magnetic data suggests that the St. Anns Leucogranite pluton is more extensive than indicated on the geological map (Barr et al., 1992).
The results of the drilling and mineral inventory studies conducted in the St. Anns area suggest that further exploration work in this area should focus on the St. Anns Leucogranite as a target for low grade-high tonnage, porphyry style Cu±Mo±Au deposits.
References
- Barr, S. M., Raeside, R. P. and Macdonald, A. S. 1985:
- Geology of the southeastern Cape Breton Highlands, Nova Scotia; in Current Research, Part B; Geological Survey of Canada, Paper 85-1B, p. 103-109.
- Barr, S. M., Jamieson, R. A. and Raeside, R. P. 1992:
- Geology, northern Cape Breton Island, Nova Scotia; Geological Survey of Canada, Map 1752A, scale 1:100 000.
- Barr, S. M., O'Reilly, G. A. and O'Beirne, A. H. 1982:
- Geology and geochemistry of selected granitoid plutons of Cape Breton Island; Nova Scotia Department of Mines and Energy, Paper 82-1, 176 p.
- Cormier, R. F. 1979:
- Rubidium/strontium isochron ages of Nova Scotian granitoid plutons; in Mineral Resources Division, Report of Activities for 1978; Nova Scotia Department of Mines, Report 79-1, p. 143-147.
- Dickie, G. 1984:
- Muskrat Brook-St Anns' properties; Billiton Canada Ltd.; Nova Scotia Department of Mines and Energy, Assessment Report 84-067.
- Fletcher, H. 1878:
- Report on the geology of part of the Counties of Victoria, Cape Breton and Richmond, Nova Scotia; Geological Survey of Canada, Report of Progress 1876-77, p. 452.
- Geological Survey of Canada 1992:
- Aeromagnetic vertical gradient map, St. Anns Harbour, Nova Scotia; NTS 11K/7, Map C41525G, scale 1:50 000.
- Riddell, J. E., Simpson, D. H. and Telford, T. M. 1968:
- Summary report on Brubec Blocks, Tarbotvale; Nova Scotia Department of Mines and Energy, Assessment Report 11K/07A 13-Q-19(01).
Appendix 1 - Nova Scotia Department of Natural Resources Diamond-Drill Hole Log NBK95-1, North Brook, Victoria County
| Hole number: |
NBK95-1 |
Elevation: |
83.8 m |
| Location: |
North Brook, Victoria County |
Azimuth: |
030° |
| 6° UTM: |
N5136540 |
Dip: |
-45° |
| 6° UTM: |
E688020 |
Proposed depth: |
50 m |
| Latitude: |
46/21/29 |
Ultimate depth: |
87.5 m |
| Longitude: |
60/33/29 |
Drilled by: |
Nova Scotia Department of Natural Resources |
| Datum: |
Mean sea level |
Geologist: |
G. J. DeMont |
| Depth m (feet) |
Description |
0-87.5 m
(0-287 ft) |
The drill core is composed primarily of pink, medium grained granodiorite, with lesser amounts of dark green, porphyritic, diabase dikes and pale pink, leucogranite dikes. The granodiorite contains fine grained, disseminated magnetite which makes the core weakly magnetic. The granodiorite exhibits a pervasive weak to intense sericite or saussurite alteration of the plagioclase feldspars. Patchy, hematized zones and variable concentrations of thin (1-5 mm), quartz±epidote±pyrite±carbonat e veinlets are visible throughout the drillhole. |
| |
0-4.70 m
(0-15.44 ft) |
Broken core composed of a mixture of pink granodiorite and dark green diabase dikes. |
| |
13.11-13.67 m
(43-44.84 ft) |
Broken core |
| |
13.11-14.51 m
(43-47.6 ft) |
Epidote-quartz veining is more common than normal in the granodiorite. The granodiorite has a bleached appearance which is possibly due to silicification. |
| |
15.42-15.49 m
(50.58-50.83 ft) |
This pink leucogranite dike contains trace amounts of disseminated pyrite. |
| |
19.18-20.03 m
(62.92-65.73 ft) |
Hematite alteration has caused a distinct reddening of the granodiorite. There is also an increase in the number of epidote veinlets cutting the granodiorite. |
| |
25.70-26.61 m
(84.32-87.3 ft): |
The granodiorite is brecciated and exhibits hematite alteration. One, white, 1-3 mm, quartz-carbonate veinlet cuts the granodiorite at an angle of approximately 80° to the core axis. This vein is discordant to the general, 45° to the core axis orientation of the epidote veinlets. |
| |
29.40-30.26 m
(96.45-99.27 ft): |
The granodiorite exhibits hematite alteration, and is brecciated or ground. |
| |
30.26-31.39 m
(99.27-103 ft): |
This is a red to dark green porphyritic diabase dike. Hematite coats slickensided fracture surfaces, and brecciated portions of the dike are cemented with a mixture of white quartz and carbonate. |
| |
32.14-32.19 m
(105.45-105.61 ft): |
This green diabase dike contains 1-3 mm wide epidote alteration zones along both contacts with the granodiorite. |
| |
35.24-36.20 m
(115.6-118.75 ft): |
Broken core: The granodiorite contains patchy, red hematite alteration zones, and fracture surfaces are coated in dark green chlorite. |
| |
46.63-48.76 m
(153-159.98 ft): |
This zone is composed of a mixture of 60%, pink granodiorite and 40%, light pink leucogranite dikes. The largest dike is 91 cm thick. The dikes contain trace amounts of disseminated pyrite, chalcopyrite, hematite and possibly molybdenite. |
| |
54.42-54.54 m
(178.54-178.93 ft): |
This is a dark green diabase dike. |
| |
54.66-54.90 m
(179.33-180.13 ft): |
This zone of granodiorite is green coloured because of an intense sericite or saussurite alteration of the plagioclase feldspars. It is cut by a network of thin (<1 mm), white quartz veinlets, and one larger (1 cm), purplish-red, quartz-hematite vein. A mixture of pyrite and chlorite coat the fracture surfaces. |
| |
56.12-56.20 m
(184.12-184.37 ft.): |
A pale pink leucogranite dike cuts the granodiorite at an angle of 60-70° to the core axis. |
| |
57.11-64.49 m
(187.38-211.60 ft): |
This darker coloured zone of granodiorite is more chloritic, has a noticeable decrease in the proportion of white feldspar crystals, and is cut by an increased number of epidote veinlets. The plagioclase feldspars exhibit patchy, light green zones of intense sericite or saussurite alteration. One, 3.8 cm thick fracture, which roughly parallels the core axis, is filled with a mixture of quartz, carbonate and purplish-red hematite. This fracture filling vein also contains traces of pyrite and chalcopyrite, and the feldspars in the granodiorite exhibit intense sericite or saussurite alteration along both contacts with this vein. |
| |
64.49-82.12 m
(211.60-269.43 ft): |
Diabase and leucogranite dikes occur near the base of this darker coloured section of granodiorite. Both the granodiorite and diabase are cut by pyrite±quartz±epidote veinlets which have a general orientation of 45° to the core axis. |
| |
73.83-73.30 m
(240.5-242.24 ft): |
This is a green diabase dike. |
| |
76.3-77.87 m
(250.41-255.48 ft): |
A 12 cm thick zone of intense epidote alteration is developed at the lower contact of this diabase dike with the granodiorite. |
| |
81.86-81.72 m
(268.11-268.58 ft): |
This pink leucogranite dike is cut by 1-3 mm wide, fracture filling epidote veinlets orientated approximately 80° to the core axis. |
| |
82.12-87.48 (EOH) m
(269.43-287 ft): |
This is a lighter coloured zone of pink, medium grained granodiorite than that described above. It is cut by both pink leucogranite and green diabase dikes, and minor epidote veining. |
| |
|
86.78-86.9 m
(284.72-285.11 ft): |
This is a green diabase dike. |
| |
|
85.06-85.18 m
(279.06-279.47 ft): |
This is a pink leucogranite dike. |
| Samples |
| Sample number |
Interval m (ft) |
Analyses |
| 95NR(01) |
54.66-54.90 m (179.33-180.13 ft) |
Petrographic |
| 95NR(02) |
19.29-19.53 m (63.30-64.06 ft) |
Petrographic |
| 95NR(03) |
31.39-31.59 m (103-103.65 ft) |
Petrographic |
| 95NR(04) |
30.34-30.45 m (99.54-99.90 ft) |
Petrographic |
| 95NR(05) |
48.02-48.41 m (157.55-158.84 ft) |
Cu, Mo, Au |
| 95NR(06) |
48.41-48.62 m (158.84-159.52 ft) |
Petrographic |
| 95NR(07) |
59.27-59.57 m (194.46-195.45 ft) |
Petrographic |
| 95NR(08) |
61.38-61.50 m (201.39-201.77 ft) |
Petrographic |
| 95NR(09) |
68.80-69.02 m (225.72-226.44 ft) |
Petrographic |
| 95NR(10) |
77.58-77.75 m (254.55-255.09 ft) |
Petrographic |
| 95NR(11) |
81.86-81.72 m (268.58-268.11 ft) |
Petrographic |
| 95NR(12) |
85.06-85.18 m (279.06-279.47 ft) |
Petrographic |
| Sample descriptions and analytical results |
| Sample number |
| 95NR(01) |
This is a sample of green, medium grained granodiorite. The green coloration is a result of intense sericite or saussurite alteration of the plagioclase feldspars. These feldspars are commonly zoned, with the cores exhibiting moderate to intense sericite alteration and the rims exhibiting moderate to intense saussurite alteration. The ferromagnesian minerals (primarily hornblende) have been partially replaced by chlorite. The granodiorite contains 1-2% disseminated magnetite, and is cut by minor, thin, fracture filling, carbonate±hematite veinlets. |
| 95NR(02) |
This is a sample of pink to red, medium grained granodiorite which has undergone weak to intense hematite alteration. Hematite replaces the plagioclase feldspars, and stains the K-feldspars in the more intensely altered areas, but in other, less intensely altered areas, the rims of zoned plagioclase crystals are replaced by hematite, while the cores exhibit intense, green sericite alteration. The ferromagnesian minerals have been partially replaced by chlorite±epidote. One speck of disseminated chalcopyrite was noted in the sample. |
| 95NR(03) |
This sample of pink to red, medium grained granodiorite exhibits weak to intense hematite alteration. The ferromagnesian minerals (primarily hornblende) exhibit partial to full replacement by chlorite±epidote. The granodiorite is cut by several, <1 mm thick, carbonate±epidote veinlets. Traces amounts of pyrite, and one speck of bornite which were noted in the sample, appear to be associated with the carbonate veining. |
| 95NR(04) |
This is sample of a dark green, fine grained, porphyritic, diabase dike. It contains 3-5% disseminated magnetite, which in places, is altered to hematite. The plagioclase phenocrysts and groundmass exhibit intense sericite alteration, and the ferromagnesian minerals have been partially replaced by chlorite±epidote. |
| 95NR(05) |
This sample of a pink leucogranite dike was crushed for geochemical analysis. The analysis returned values of: 65 ppm Cu, <10 ppm Mo, and 21 ppb Au. |
| 95NR(06) |
This sample is composed of a mixture of pink, medium grained granodiorite and pale pink leucogranite. The leucogranite, which intruded the granodiorite, is comprised primarily of granophyre, with only trace amounts of ferromagnesian minerals. Plagioclase feldspars in the granodiorite exhibit weak to moderate, sericite±saussurite alteration. Epidote±quartz±chlorite±pyrite veinlets cut both the leucogranite and granodiorite. The ferromagnesian minerals in the granodiorite (primarily hornblende) are partially replaced by chlorite±epidote. The leucogranite contains trace amounts of fine grained, disseminated hematite, pyrite and chalcopyrite. |
| 95NR(07) |
This is a sample of pink, medium grained granodiorite. It is cut by several, <1 mm, quartz-epidote veinlets, some of which contain disseminated pyrite±chalcopyrite. The plagioclase crystals generally exhibit weak sericite alteration, and a small percentage of crystals have been partially replaced by epidote. The ferromagnesian minerals have been partially replaced by chlorite±epidote. |
| 95NR(08) |
This is a sample of pink, medium grained granodiorite. It is cut by a network of pale green, quartz±epidote±chlorite veinlets which contain <1% disseminated pyrite, and traces of chalcopyrite, bornite and molybdenite. The pyrite is also found as disseminations in the granodiorite. |
| 95NR(09) |
This is a sample of pink, medium grained granodiorite. It is cut by several, 1-2 mm quartz±pyrite±epidote veinlets which are oriented approximately 45° to the core axis. The plagioclase feldspars exhibit weak to moderate saussurite alteration, and the ferromagnesian minerals have been fully, or partially, replaced by chlorite±epidote. |
| 95NR(10) |
This is a sample of a dark green, porphyritic diabase dike. |
| 95NR(11) |
This sample is composed of a mixture of pink, medium grained granodiorite and a pale pink, leucogranite dike. The leucogranite, which intruded the granodiorite, is composed primarily of granophyre, with little or no mafic component. It contains trace amounts of disseminated magnetite, hematite and chalcopyrite. Both the dike and the granodiorite are cut by a pale green, fracture filling, epidote-quartz veinlet oriented approximately 80° to the core axis. This fracture displaces the intrusive contact by approximately 2 cm. |
| 95NR(12) |
This sample is composed of pink, medium grained granodiorite and pale pink leucogranite dike. The granodiorite contains an inclusion of a grey dioritic rock. The leucogranite contains one cluster of pyrite and epidote, and the granodiorite contains <0.5% disseminated pyrite. The granodiorite is cut by minor, thin (<1 mm), epidote±pyrite±quartz veinlets. |
Appendix 2 - Figures
Figures: (Not presently available)
Figure 1. Study area location map.
Figure 2. Drillhole location map, scale 1:10 000.
|
