Abstract
The Koka gold deposit is located in the Elababu shear zone between the Nakfa terrane and the Adobha Abiy terrane, NW Eritrea. Based on a paragenetic study, two main stages of gold mineralization were identified in the Koka gold deposit: (1) an early stage of pyrite–chalcopyrite–sphalerite–galena–gold–quartz vein; and (2) a second stage of pyrite–quartz veins. NaCl-aqueous inclusions, CO2-rich inclusions, and three-phase CO2–H2O inclusions occur in the quartz veins at Koka. The ore-bearing quartz veins formed at 268 °C from NaCl–CO2–H2O(–CH4) fluids averaging 5 wt% NaCl eq. The ore-forming mechanisms include fluid immiscibility during stage I, and mixing with meteoric water during stage II. Oxygen, hydrogen, and carbon isotopes suggest that the ore-forming fluids originated as mixtures of metamorphic water and magmatic water, whereas the sulfur isotope suggests an igneous origin. The features of geology and ore-forming fluid at the Koka deposit are similar to those of orogenic gold deposits, suggesting that the Koka deposit might be an orogenic gold deposit related to granite.
Highlights
The Nubian Shield, located in northeastern Africa, is an important Gondwana metallogenic domain [1,2] that formed during the Neoproterozoic Pan-African orogenic cycle [2,3].Most of the Volcanic-associated Massive Sulfide (VMS) type and quartz vein-hosted gold ± sulfide deposits and occurrences in Eritrea are concentrated along NNW- and NNE-trending narrow zones in the south Nubian Shield [4]
Both the world class Bisha VMS and Koka gold deposits are located in the Adobha Belt (AAB) copper and gold metallogenic belt [6,7]
In order to understand the genesis of the Koka deposit, we conducted a detailed study of deposit geology, fluid inclusions (FIs), quartz C–H–O isotopes, and the sulfide S isotope of the Koka gold deposit to better constrain the fluid and metal source, ore-forming fluid evolutionary history, and genesis
Summary
The Nubian Shield, located in northeastern Africa, is an important Gondwana metallogenic domain [1,2] that formed during the Neoproterozoic Pan-African orogenic cycle (ca. 900–550 Ma) [2,3]. Most of the Volcanic-associated Massive Sulfide (VMS) type and quartz vein-hosted gold ± sulfide deposits and occurrences in Eritrea are concentrated along NNW- and NNE-trending narrow zones in the south Nubian Shield [4]. Both the world class Bisha VMS and Koka gold deposits are located in the AAB copper and gold metallogenic belt [6,7]. The Koka gold deposit is located in northwest Eritrea, which has a long mining history that extends back to the Egyptian Pharaohs. In order to understand the genesis of the Koka deposit, we conducted a detailed study of deposit geology, fluid inclusions (FIs), quartz C–H–O isotopes, and the sulfide S isotope of the Koka gold deposit to better constrain the fluid and metal source, ore-forming fluid evolutionary history, and genesis
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