3. Adane Hailu

109 Pages·2017·4.79 MB·English

I
SOME FEATURES OF GOLD MINERALIZATION
IN SOUTHERN SEKEN 1 AREA (WORQ AMBA),
.
TIGRAY
AThesis Submitted to the School of Graduate Studies of Addis Ababa
University in PartialFulfillment of theRequirements for the Degree of
Master of Science in Geology.
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1 LI fi R A R ! S
By Tenicsgen Qfgaa
-
June, 2000.
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I would like to express my gratitude to Dr. Worash Getaneh , my advisor, for his
advice and assistances during this work. Furthermore, his comments on the draft of
thisdocument was invaluable.
I am glad also to take this opportunity to thank the Department of Geology and
Geophysics, Addis Ababa University, and all members of the academic staff of the
Department for their cooperations.
Particularly, Dr. Teklewold Ayalew and Dr. Mulugeta Alene of the Department of
Geology and Geophysics are thanked for their important and constructive
discussions. Additionally, the former hasassisted in supplyingsome books and other
documents relevant to thestudies.
Ministry of Mines and Energy of the Federal Democratic Republic of Ethiopia and
National Mining Corporation"pic (NMC) are thanked for permitting access to the
study area and to the relevant information, without which this study would have not
been realized.
Additionally, the author is grateful to NMCfor covering transportation costs to and
from the study area, and part of sample preparation costs. The cooperations of the
higher officials, professional personnel and administrative personnel in the Mekele
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branch office of NMC is heartily appre<<ciate(iJdf l.;13< Tt>ijlfjlelctl;‘t5»)geftlo:tilitcog<(cttfif«s«ttsCcc<c:if <fH(ctk?r'icffr{p{>ar<i<(titc<tcr.u(latrtfcltyt
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thanked for their invaluablediscussions in the field. (cid:127)
1 1 :
I am indebted to the Ethiopian Institute of Geological Surveys for its permission to
conduct the chemical analyses, thin and polished sections preparations and
microphotography free of charge. Thanks are extended particularly to Workelul
Gebrekiristos, AdisieMekonen and Mesfin Tesema of the Mineralogical Laboratory
for their invaluabletechnical assistancesand friendly cooperations.
i
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Table of Contents
Page
Acknowledgment -
I
Table ofcontents
Ill
List of tables
V
List of figures
VI
Listof plates
VII
Abstract - - VIII
.
1 Introduction
1
1.1 Location and Accessibility - 1
1.2 Climate, Vegetation and Population - 2
1.3 Previous Work
4
—
1.4 Objectives ofthePresent Work
14
1.5 Methods -
15
.
2 Geology -
17
2.1 Regional Geological Setting -
17
2.1.1 Introduction - 17
2.1.2 Basement geology ofTigray - 22
2.1.3 Geology of Worq Amba 25
2.2 Local Geology
30
2.2.1 Feldspar quartzsericiteschist 30
2.2.2 Muscovitechloriteschist 35
2.2.3 Basic metavolcanics - 36
III
2.2.4 Granodiorite
38
—
2.2.5 Graniticdykes - 41
2.2.6 Quartz veins 42
2.2.7 Carbonateveins - 43
2.3 Wall rock alterations 46
2.4 Structure 52
—
2.5 Metamorphism 55
.
3 Geochemistry 57
3.1 Analytical procedure - 57
3.2 Major elements - 58
3.2.1 Granodiorite 58
3.2.2 Chlorite talcschist - 60
3.2.3 Feldspar quartzsericiteschist 60
—
-
3.3 Trace elements 63
3.3.1 Distribution of traceelements 67
—
3.3.2 Association ofelements 71
.
4 Gold Mineralization 78 -
4.1 Sulfide mineralization 80
4.2 Fluid characteristics 81
.
5 Relationship between thegranodioriteand mineralization 86
.
6 Conclusion and Recommendations 88
References - - 93
IV
List of Tables
Page
Table 1. Major element composition ofselected samples 58
Table 2. Averagecomposition ofgranodioriterecalculated by
excludingL.O.I.
59
Table3. Averagecomposition of muscovite-biotitegranodiorite- 59
Table 4. Averagecomposition ofsome metamorphicrocks on
—
anhydrousbase
61
Table5. Composition offeldspar quartzsericiteschist
recalculated onanhydrousbase 62
Table 6.Description ofsamples -
64
Table 7. Analysis results ofsome trace elements 66
Table 8. Averageconcentrationsofsomeelementsin common
crustal rocks -
67
V
.
...
List of Figures
Page
Figure 1.1 Location map of thestudy area 3
Figure 1. 2Sketch diagram ofDl & D2 folds - - 8
Figure 1.3 Location Map of Seken 1 and Seken 2 12
Figure 1.4 Map showing gold bearingzone - 13
—
Figure 2.1 Simplified geological mapofMai Kenetal-Negash area 29
Figure2.2 Geological map ofSouthern Seken 1 34
Figure2.3 Field sketch ofsmall folds 56
Figure3.1 Sample location map - - 65
Figure3.2Scatterdiagram ofgold vsotherelements 75
VI
!(cid:127)-
List of Plates
Page
Plate 1.Photomicrograph offeldspar quartzsericiteschist 33
Plate2.Photomicrograph of muscovitechloriteschist 37
Plate 3.Photomicrograph showing somefeaturesof
thegranitedyke and granodiorite —
40
Plate 4.Photomicrograph showingcarbonatevein
—
and carbonatization in plagioclase - 45
Plate5.Photomicrographshowingsomealteration features
in granodioriteand feldspar sericiteschist
51
Plate6.Photomicrograph showingoccurrenceof
pyrite mineralization
85
VII
Abstract
Some features of gold mineralization in the Southern Seken 1 area (Worq Amba),
Tigray have been studied.
The geology of the study area is constituted by feldspar quartz sericite schist,
muscovite chlorite schist, basic metavolcanics and granodiorite. The feldspar quartz
sericite schist consists of thin intercalations of strongly silicified and chlorite talc
schist. Additionally,granitic dykes and carbonate veins occur in this rock parallel to
the regional foliation. The muscovite chloriteschist also has intercalations of quartz
chlorite schist along its western margin. Major and minor quartz veins also occur in
all major rocks. Foliations generally strike to the northeast and dip at moderate to
steep angles to thewest.Other geological structuresevident in the study area include
fractures and small tight folds. These folds may represent the earliest phase folds in
thearea.
The rocks are strongly affected by hydrothermal alterations. Wall rock alteration
types evident in the area include sericitization, silicification, carbonatization,
chloritization, epidotization and sulfidation.
Gold mineralization might have resulted from hydrothermal processes that caused
the wall rock alterations. Open spaces along host rockfractures and foliations might
have provided channel ways for the hydrothermal fluid. Gold has been detected in
quartz and carbonate veins and altered feldspar quartz sericite schist, muscovite
chloriteschist. The highest gold content has beenobtained in chloritetalcschist that
is intercalated in feldspar quartz sericiteschist.
VIII
Gold shows a slight positive correlation with cobalt. Though this result is not
sufficient to suggest the source of the gold to be mafic-ultramafic rocks, it attracts
attention for furtherstudies in thisregard.
Some evidences from thegranodiorite reveal that it is unlikely that the hydrothermal
fluid emanated from this intrusive body.
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