Proterozoic A-Type Granitoids And Volcanic Rocks

Proterozoic A-Type granitoids and volcanic rocks that make the basement to the Central African Copperbelt, Zambia
Alberto Lobo-Guerrero S.
Geologist, M.Sc., Min.Ex, Ph.D. Operations Vice-President LOGEMIN S.A. Bogotá, Colombia; www.logemin.com

About the Speaker
Geologist, Geosciences Department, Universidad Nacional de Colombia, Bogotá M.Sc. in Mineral Exploration Geology, Queen´sUniversity, Kingston, Ontario, Canada Outer Space Specialist, International Space University Strasbourg, France Ph.D. in Geology, Economic Geology Research Institute, University of the Witwatersrand, Johannesburg, South Africa Currently consultant in exploration and mining actitivies at LOGEMIN S.A., Bogotá, Colombia.

Proterozoic A-Type granitoids and volcanic rocks that make the basement to theCentral African Copperbelt, Zambia
Alberto Lobo-Guerrero S.
Geologist, M.Sc., Min.Ex, Ph.D. Operations Vice-President LOGEMIN S.A. Bogotá, Colombia; www.logemin.com

Take-home message

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1 Zambian Copperbelt basement = several generations of Proterozoic A-type porphyritic rocks & associated volcanics 2 Most granitoids display rapakivi features 3 Plutonics & volcanics show similarage & chemistry 4 Clearly an anorogenic ring complex cluster -with 4 distinct overprinted Proterozoic ARCC events 5 Main rock types: granites, alkali granites, qtzmonzonites & gabbroids 6 Complex geological history, alteration, metamorphism 7 Possible relationships between basement rks, IOCG mnzn & sed-hosted Cu mnzn 8 Basement hosts hypogene Cu mnzn veins & disseminations 9 Tricky macroscopiccorrelation -due to similar rock suites from different ages

Proterozoic A-Type granitoids & volcanic – Copperbelt basement

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Contents
-1 Introduction Location General geology Anorogenic character -2 TAS diagram -3 Event diagram -4 Main Units in Copperbelt basement -5 Hydrothermal alteration -6 Mineralization -7 Macroscopic Correlation? -8 Conclusions

LOGEMIN S.A.Introduction 1
Zambian Copperbelt = one of t’ world’s most prolific Cu provinces, composed by series of A-Type plutonic rocks & their correlative meta-volcanics.

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Zambia In southern Africa

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Location of the Zambian Copperbelt

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Copperbelt Generalized Geology

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Basement rocks in Zambian Copperbelt

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Introduction 2Basement rocks in t’ environs of t’ Copperbelt & intrusives that cut Katangan sedimentary sequence are all anorogenic.

Most granitoids display rapakivi features.

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A-type character of Copperbelt basement granitoids (a few of the diagrams by Whalen et al, 1987)

K2O/MgO

K2O + Na2O

10

10 9 8 7 6

1

5 4 3 1
2 3 4 5 6 7 8 9

10

1

2

3

4

5

6

78 9

10

10,000*Ga/Al

10,000*Ga/Al

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Proterozoic A-Type granitoids & volcanic – Copperbelt basement

Contents
-1 Introduction -2 TAS diagram -3 Event diagram -4 Main Units in Copperbelt basement -5 Hydrothermal alteration -6 Mineralization -7 Macroscopic Correlation? -8 Conclusions

Modified TAS diagram (After Middlemost, 1994)

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19

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18

TAS Diagram for Rocks in the 17 Basement, Zambian CuBelt, Africa
(Data from Lobo-Guerrero, 2005) 16
Curves of Sigma Index values Petrographic fields 15 Muliashi Porphyry Lufubu Schists 14 Chambishi Mine environs Mufulira Granite and other rocks 13 Schist of the Samba Cu deposit Nchanga Granite granitoids 12 Nchanga Mine other intrusives

X-40

X-39 P-28

Na 2 O% + K 2 O%

11 109 8 7 45 6
L-1 67a L-1 61

KN S1

Ba4 Ba5 X-09

P-29

Nchanga Granite
X-01 L -17 L-17 2 3 NG2 L-151 L-1 54 NG5 -16 2 L L-153 NG3 N G4 X-34a X-34 X-3 6 L-168 Ba2 L-158 Ba1 X-35

L-1 50

Muliashi-Lufubu Suite
X-41 BN5 3/1

Ba6 L-077 L-166 NG6 L-160 NN 75/1 Cham bish i Granite L -15 L-0 78 9 X-03

X-02

L -07 5 6

X-05

Ba3

MN 153 MN 154 X-0 6 X-1 1 X-14

X-08 L -27 9...