Glacial dispersion of refractory minerals from the Gibraltar porphyry copper deposit, southcentral British Columbia, Canada

1 1 2L. Wolfe , K. Hattori , A. Plouffe1Department of Earth and Environmental Sciences, University of Ottawa, 25 Templeton Street, Ottawa, Ontario, K1N 6N5;

2Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario , K1A 0E8

Study area The Gibraltar porphyry Cu-Mo mine is the second largest

open pit in Canada with reserves of 1.74 Mt Cu. The Gibraltar deposit is hosted by the Late Triassic Granite Mountain batholith, comprised primarily of tonalite and diorite with minor variations in abundance in minerals (Kobylinski et al., 2016). The mine has three pits central to our study area; Gibraltar, Pollyanna and Granite (Fig. 1-A). The batholith intruded into Nicola Group volcanic rocks in the western limit of the Quesnel Terrane near the boundary with the Cache Creek terrane. Nicola Group rocks are composed primarily of volcanic rocks that have been metamorphosed under greenschist facies conditions (Schiarizza et al., 2014). Cache Creek terrane rocks are composed of chemical and siliclastic rocks (Schiarizza et al., 2014). The region is in large part covered by till deposited during three phases of glaciation with ice flows towards southeast, southwest and north to northwest (Fig. 1-A) (Plouffe et al., 2014).

Rutile Zircon Epidote

Summary - Trace element concentrations of rutile can be used to identify samples associated with mineralization

- Zircon grains are all igneous in origin.

- Zircon crystallized in both oxidized and reduced magma

- Epidote shows a compositional variation from Fe-rich epidote to Al-rich clinozoisite site

- Al-rich epidote is similar to that from the mine site reported by Kobylinski et al. (2016)

- Rutile, zircon and epidote have similar compositions throughout the study sites independant of the proximity and directions to the Gibraltar mine, suggesting that the glacial dispersion of minerals was greater in distance.

Introduction Drift prospecting examines the spatial distribution of minerals

with specific chemistry in streams and glacial sediments. This method allows geoscientists to locate distal mineral deposits that may be covered by overburden. This project evaluates the feasibility of indicator mineral exploration for porphyry copper deposits using heavy minerals in tills. For this project, we selected the area near the Gibraltar porphyry Cu-Mo mine in south central British Columbia.

Rutile grains have a composition close to the end member with >99 wt.% TiO . 26 rutile grains analysed by LA-2

ICP-MS have average trace element concentrations of 3970 ppm Fe, 2800 ppm Nb, 1220 ppm V and 658 ppm W. Inclusions of ilmenite occur in 16 out of 64 grains (Fig. 2). The i lmenite i n c l u s i o n s a r e c o m p o s e d o f approximately 35-45 wt.% FeO(t) with up to 2 wt.% MnO.

Samples Heavy minerals were separated from ca. 10 kg of till samples

at each site.Total of 440 grains from basal tills: Rutile (64 grains from 5 sample sites), epidote (185 grains from 4 sample sites) and zircon (191 grains from 5 samples sites). Sample sites were selected to examine mineral dispersion patterns from the deposit

Analytical methods1. Optical examination2. SEM-EDS, CL-SEM3. EPMA 4. LA-ICP-MS

Grains of epidote are Ca-rich (ca. 23 wt%) with varying Fe O (t) (12-20 2 3

wt.%). The 93 grains analysed show the total REE contents up to 0.1 wt.% (Fig. 4-2). Approximately 40% of epidote grains contain mineral inclusions of titanite. Titanite contains a variance of Al O between 1 and 5 wt.%, 2 3

suggesting that they are mostly hydrothermal in origin. Other mineral inclusions are zircon, quartz, apatite, magnetite and actinolite.

Fig. 1-A

Fig. 2-1: SEM-BSE image of rutile grain #6 from sample site 12PMA-056-A01. Th is ru t i le gra in d isp lays typ ica l ilmenite inclusions and homogeneousrutile composition.

Fig. 2-4: Rutile samples 11PMA-024-A2, 11PMA-

038-A1 and 12PMA-536-A01 plot in the high-grade ore field of the El Teniente porphyry Cu deposit by Rabbia et al. (2010).

/

.001

.01

.1

1

10

100

1000

10000

LaCe

PrNd

PmSm

EuGd

TbDy

HoEr

TmYb

Lu

X/C

hond

rites

Zircon (45 grains) 12PMA-522-A01

12TFE-75-A01

12PMA-024-A02

12PMA-032-B01

11PMA-056-A01

Chondrite values after McDonough and Sun (1989)

Zircon grains have subhedral to euhedral crystal habit with many inclusions (Fig. 3-1). Images of CL-SEM show oscillatory zoning, indicating igneous origin of the grains. Most grains (95%) display sector zoning (Fig. 3-B). Chondrite-normalized REE patterns are similar among all grains (Fig. 3-2).

0 10 20 300.2

0.3

0.4

0.5

0.6

Eu/

Eu*

Ce/Nd

Zircon (45 grains)

Apatite

Sector zoning

AcknowledgmentsThis research project is supported by the Geological Survey of Canada through the Targeted Geoscience Initiative 5 (TGI-5) program. We also thank the Society of Economic Geologists Canada Foundation for their support to LW. We thank Glenn Poirier and Samuel Morfin for their help during the SEM, EPMA and LA-ICP-MS analyses.

ReferencesFerry, J.M., Watson, E.B. (2007). New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers. Contributions to Mineralogy and Petrology,154: 429-437. doi:10.1007/s00410-007-02010

Kobylinski, C.H., Hattori, K., Smith, S., and Plouffe, A., 2016. Report on the composition and assemblage of minerals associated with the porphyry Cu-Mo mineralization at the Gibraltar deposit, south central British Columbia, Canada; Geological Survey of Canada, Open File 8025, 30 p. doi:10.4095/298804

McDonough, W.F., Sun, S.s. (1989). Composition of the Earth's primitive mantle. 223-253.

Meinhold, G. 2010. Rutile and its applications in earth sciences. Earth-science reviews, 102: 1-28.

Plouffe, A., Ferbey, T., and Anderson, R.G., 2014. Till composition and ice-flow history in the region of the Gibraltar Mine: developing indicators for the search of buried porphyry mineralization; Geological Survey of Canada, Open File 7592, 1 poster. doi:10.4095/293839

Plouffe, A., Ferbey, T., Anderson, R.G., Hashmi, S., Ward, B.C., and Sacco, D.A. 2013. The use of till geochemistry and mineralogy to explore for buried porphyry deposits in the Cordillera – preliminary results from a TGI-4 Intrusion-related Ore Systems Project; Geological Survey of Canada, Open File 7367, poster. doi: 10.4095/292555

Rabbia, O.M., Hernandez, L.B., French, D.H., King, R.W. & Ayers, J.C. 2009. The El Teniente porphyry Cu-Mo deposit from a hydrothermal rutile perspective. Mineralium Deposita, 44: 849–866.

Schiarizza, P., 2014. Geological setting of the Granite Mountain batholith, host to the Gibraltar porphyry Cu-Mo deposit, south-central British Columbia. In: Geological Fieldwork 2013, British Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper 2014-1, pp. 95-110.

700 750 800 850 9000

10

20

30

CN

d

Temperature (°C)

Zircon (45 grains)

100*Fe+Cr+V 1000*Sn+W

Ti

12PMA-536-A01

11PMA-024-A02

12PMA-056-A01

12PMA-042-A01

11PMA-038-A1

Rutile (26 grains)Fig. 2-2

15 16 17 18.01

.1

1

Sc

+Y

+La

+C

e(w

t.%

)

Ca (wt.%)

12PMA-539-A01

12PMA-540-A01

12PMA-053-A01

12PMA-056-A01

Epidote (93 grains)

Epidote group general formula: A2M3[T2O7][TO4](O,F)(OH,O)

0.8 0.9 1.0 1.10.00

0.02

0.04

0.06

0.08

0.10

Sr

+M

n+

Pb

(cation

units)

Ca (cation units)

Epidote A site (93 grains)

1.8 1.9 2.0 2.1 2.2 2.3 2.40.6

0.7

0.8

0.9

1.0

1.1

1.2

Fe

+T

i+M

n+

V(c

atio

nunits

)

Al (cation units)

Epidote M site (93 grains)

Fig. 2-2: Rutile contains up to 1 wt.% W averaging 658 ppm W.

Rutile (26 grains)

400 500 600 700.001

.01

.1

1

10

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Mo/Sb

Temperature (°C)

Low-grade ore

High-grade ore

Rutile (26 grains)

Fig. 2-3

100 1000 10000 1000001

10

100

1000

10000

Cr (ppm)

Nb (ppm)

Rutile (26 grains)

Rutile from metapeliticrocksRutile from

metamafic rocks

Rutile

Ilmenite

.1 1 10 100 1000.1

1

10

100

1000

Mo (ppm)

Sb (ppm)

Rutile (26 grains)

Low-grade ore

High-grade ore

Fig. 2-4

Fig. 2-3

After Plouffe et al. (2013)

Fig. 3-1

Fig. 2-1

Results - mineral chemistry

Fig. 3-1B

Fig. 3-2Fig. 4-2

Fig. 2-5: Zr content in rutile ranges from 18-535 ppm. Crystallization temperatures range from 4 6 0 t o 7 0 0 ° C u s i n g Z r - i n - r u t i l e geothermometry by Ferry et al. (2007).

Samples 11PMA-024-A2, 11PMA-038-A1 and 12PMA-536-A01 plot in the high-grade ore field of the El Teniente porphyry Cu deposit by Rabbia et al. (2010).

Fig. 3-1B: CL-SEM image of zircon grain #32 from sample site 11PMA-024-A02.

Fig. 2-5

Fig. 3-3

Fig. 3-4

/ e

oxidizedmagama

reducedmagama

Fig. 4-1B

Fig. 3-4: Ti content in zircon ranges from 5-19 ppm. Crystallization temperatures range from to 713 to 8 4 7 ° C u s i n g Ti - i n - z i r c o n geothermometry by Ferry et al. (2007) assuming activity of 0.7 for TiO and 1 as the activity for SiO . 2 2

Actinolite

Fig. 4-1: SEM-BSE image of epidote grain #14 from sample site 12PMA-540-A01.

Titanite

Fig. 4-1

Fig. 4-1B: SEM-BSE image of epidote grain #1 from sample site 12PMA-053-A01.

Fig. 4-3

Fig. 4-4

Fig. 4-4: Epidote with high-Al and low-Fe is considered to be a s s o c i a t e d w i t h s u l p h i d e mineralization.

Fig. 2-3: Rutile samples are sourced from both

metapelitic and metamafic rocks according to the discrimination from Meinhold et al. (2009).

12PMA522A01

12TFE075A01

11PMA024A02

12PMA032B01

12PMA056A01