Structural controls of fluid flow and gold mineralization in the easternmost parts of the Karagwe-Ankole Belt of north-western Tanzania

Structural controls of fluid flow and gold mineralization in the easternmost parts of the... Gold mineralization in the Biharamulo region of western Tanzania is confined to the sheared, low-angle basement-cover contact between Archaean basement gneisses of the Tanzania Craton and the structurally overlying, low-grade metamorphic metasediments of the Mesoproterozoic Karagwe-Ankole Belt. Regional-scale fluid flow along this detachment is indicated by the pervasive silicification and retrogression of wall rocks to pervasively foliated phyllonites and pyritization of particularly metasediments, commonly graphite-rich, in the hanging wall of the shear zone. Gold mining centres on specific structural sites along the detachment, but also in stratigraphically higher sections in the structurally overlying metasediments. Zones of gold mineralization along the detachment correlate with NE trending ramp structures (dip angles 20°–35°) that are most ideally orientated for slip and reactivation within the low-angle phyllonitic detachment. Repeatedly overprinted auriferous quartz-vein stockworks in quartzofeldspathic gneisses immediately below the detachment indicate brittle fracturing of the competent footwall lithotypes during slip along the weaker detachment. In cases of massive silicification, up to 50m thick quartz blows are formed along the contacts between detachment phyllonites and footwall gneisses. The multiple overprinting relationships of successive quartz-vein generations in these zones of massive silicification suggests that the quartz blows acted as competent blocks in the weak detachment, causing the repeated overprint of earlier silicification by later fracturing and quartz-veining events. Gold mineralization above the detachment and in stratigraphically higher metasediments is closely associated with fold structures that form part of the low-grade metamorphic fold-and-thrust belt. Veining is particularly abundant in competent lithotypes, such as quartzite and chemically reactive ferruginous mafic sills. Overprinting relationships between quartz vein sets illustrate fluid flow during fold amplification and, importantly, the final lock-up stage of folds, during which much of the mineralization was introduced. Oxygen isotope values for quartz veins indicate fluids were likely derived from clastic, mainly metapelitic sedimentary sequences of the Karagwe-Ankole Fold Belt. The data also implies that the partially reworked Archaean granitoid-greenstone basement of the Tanzania Craton has not contributed to the fluid evolution and possibly gold mineralization. The extent (>100km) of the basement-cover detachment and associated alteration is indicative for a regional-scale fluid system. Gold mineralization is, however, controlled by local structures and lithological contrasts that require the detailed mapping and sampling of the regional structure. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ore Geology Reviews Elsevier

Structural controls of fluid flow and gold mineralization in the easternmost parts of the Karagwe-Ankole Belt of north-western Tanzania

Loading next page...
 
/lp/elsevier/structural-controls-of-fluid-flow-and-gold-mineralization-in-the-KiGYuUpj2K
Publisher
Elsevier
Copyright
Copyright © 2016 Elsevier B.V.
ISSN
0169-1368
eISSN
1872-7360
D.O.I.
10.1016/j.oregeorev.2016.03.010
Publisher site
See Article on Publisher Site

Abstract

Gold mineralization in the Biharamulo region of western Tanzania is confined to the sheared, low-angle basement-cover contact between Archaean basement gneisses of the Tanzania Craton and the structurally overlying, low-grade metamorphic metasediments of the Mesoproterozoic Karagwe-Ankole Belt. Regional-scale fluid flow along this detachment is indicated by the pervasive silicification and retrogression of wall rocks to pervasively foliated phyllonites and pyritization of particularly metasediments, commonly graphite-rich, in the hanging wall of the shear zone. Gold mining centres on specific structural sites along the detachment, but also in stratigraphically higher sections in the structurally overlying metasediments. Zones of gold mineralization along the detachment correlate with NE trending ramp structures (dip angles 20°–35°) that are most ideally orientated for slip and reactivation within the low-angle phyllonitic detachment. Repeatedly overprinted auriferous quartz-vein stockworks in quartzofeldspathic gneisses immediately below the detachment indicate brittle fracturing of the competent footwall lithotypes during slip along the weaker detachment. In cases of massive silicification, up to 50m thick quartz blows are formed along the contacts between detachment phyllonites and footwall gneisses. The multiple overprinting relationships of successive quartz-vein generations in these zones of massive silicification suggests that the quartz blows acted as competent blocks in the weak detachment, causing the repeated overprint of earlier silicification by later fracturing and quartz-veining events. Gold mineralization above the detachment and in stratigraphically higher metasediments is closely associated with fold structures that form part of the low-grade metamorphic fold-and-thrust belt. Veining is particularly abundant in competent lithotypes, such as quartzite and chemically reactive ferruginous mafic sills. Overprinting relationships between quartz vein sets illustrate fluid flow during fold amplification and, importantly, the final lock-up stage of folds, during which much of the mineralization was introduced. Oxygen isotope values for quartz veins indicate fluids were likely derived from clastic, mainly metapelitic sedimentary sequences of the Karagwe-Ankole Fold Belt. The data also implies that the partially reworked Archaean granitoid-greenstone basement of the Tanzania Craton has not contributed to the fluid evolution and possibly gold mineralization. The extent (>100km) of the basement-cover detachment and associated alteration is indicative for a regional-scale fluid system. Gold mineralization is, however, controlled by local structures and lithological contrasts that require the detailed mapping and sampling of the regional structure.

Journal

Ore Geology ReviewsElsevier

Published: Sep 1, 2016

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 12 million articles from more than
10,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Unlimited reading

Read as many articles as you need. Full articles with original layout, charts and figures. Read online, from anywhere.

Stay up to date

Keep up with your field with Personalized Recommendations and Follow Journals to get automatic updates.

Organize your research

It’s easy to organize your research with our built-in tools.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

Monthly Plan

  • Read unlimited articles
  • Personalized recommendations
  • No expiration
  • Print 20 pages per month
  • 20% off on PDF purchases
  • Organize your research
  • Get updates on your journals and topic searches

$49/month

Start Free Trial

14-day Free Trial

Best Deal — 39% off

Annual Plan

  • All the features of the Professional Plan, but for 39% off!
  • Billed annually
  • No expiration
  • For the normal price of 10 articles elsewhere, you get one full year of unlimited access to articles.

$588

$360/year

billed annually
Start Free Trial

14-day Free Trial