The in-country operating entity is Gramalote Colombia Limited (Gramalote Colombia”). On October 5, 2023, B2Gold acquired the remaining 50% interest of the Gramalote Project owned by AngloGold resulting in B2Gold owning 100% of the Gramalote Project.
Summary:
The Gramalote Ridge and Trinidad deposits are considered to be examples of structurally-controlled intrusive-related gold deposits.
Intrusive-related gold deposits have many synonyms, including Intrusion-related gold systems, gold porphyries, and plutonic-related gold quartz veins. The deposit model that follows is abstracted from Lefebure and Hart (2005).
The deposit shows a number of the features of intrusive-related gold deposits, including:
• Alteration and mineralization are structurally controlled, restricted to small haloes along veins, sheeted veins and stockworks arrays;
• Sulphides content is less than 5%;
• Some evidence indicates that the host rock is directly related to fluids evolved from the cooling pluton, including pegmatite, aplite and K-feldspar alteration (Rodríguez, 2009).
The QP is of the opinion that exploration programs that use a structurally-controlled, intrusive-related gold model are applicable to the Project area.
The Project is located in the northern portion of Colombia’s Central Cordillera. The terrane primarily comprises a metamorphic basement complex and the Antioquia Batholith. The Cajamarca–Valdivia basement terrane (Cediel and Ciceres, 2000 and Cediel et al, 2003) consists of early Paleozoic metamorphic rocks; as well as ophiolitic, oceanic, volcanic, and intrusive rocks.
In the general Project area, the main compositional types within the Antioquia Batholith are tonalite and granodiorite, with subordinate monzonite and gabbro. Alaskitic, felsitic and andesitic dikes have intruded the complex. Age dating conducted by AngloGold suggest the gold mineralization is associated with the last stages of batholith crystallization.
Gramalote Ridge is situated between two west–northwest-trending macro-scale curved lineaments that splay off the Palestina fault to the east, and transect the Antioquia Batholith, termed the Nus River and the El Socorro lineaments. Differential movement along the Nus and El Socorro lineaments is thought to have generated north–northwest, north–south and northeast-striking tensional dilation within the tonalite, reflected in the formation of stockwork style sheeted quartz and quartz carbonate veinlets.
Gramalote Ridge
The Gramalote Ridge deposit has dimensions of 1,300 by 1,500 by 700 m. The mineralization has been drill-tested to a depth of about 650 m.
Mineralization at Gramalote Ridge is hosted in uniform medium-grained tonalite with minor amounts of granodiorite and aplite dykes.
Alteration is structurally-controlled and occurs as both broad zones and narrow selvedges around veins. At Gramalote Ridge, vein selvedges range from a few millimetres up to as much as 10 cm. The broader alteration zones mimic the vein selvedges and progress from an outer quartz–sericite zone to inner carbonate and potassic zones.
Gramalote Ridge mineralization occurs within several zones that periodically coalesce both along strike and down-dip. Zones vary in width from 10–150 m in true width with vertical to sub-vertical dips to the south–southeast. The deposit remains open at depth and along strike.
Anomalous gold grades are associated with three overprinting, texture-destructive alteration assemblages including potassic, quartz–sericite and sericite–carbonate. The magnetite-destructive alteration characteristics of these zones is clearly defined from airborne and ground magnetic surveys over the tonalite host rock, which is weak to moderately magnetic.
The mineralization is vein-hosted, either in sheeted veins or in local stockworks, and is structurally-controlled.
Three stages are identified and associated with vein and alteration types:
• Quartz–calcite–pyrite is an assemblage of fine-grained quartz and calcite with very fine-grained pyrite. This vein type generally does not host gold;
• Quartz–pyrite–chalcopyrite–gold is the most important gold host, typically associated with K-feldspar (potassic) selvedge. The gold occurs in fractures in pyrite together with chalcopyrite;
• Quartz–calcite–white mica is commonly barren but can show moderate gold grades. The veins are typically identified through the selvedge of white mica.
Veinlets have been classified into seven types. Anomalous gold mineralization is associated with Type 1 (Quartz ± pyrite), Type 2 (Quartz + carbonate + pyrite + chalcopyrite) and Type 5 (Coarse pyrite + quartz) vein types, with Type 1 and Type 2 the most prevalent.
Mineralization in saprolite and saprock (oxide) is weathered insitu and does not show evidence of significant transport or displacement. Weathered mineralization is limited to the areas directly above fresh mineralization and represents a small percentage of the mineralization. Saprolite/saprock thickness is variable from 5–50 m, with an average thickness of 21 m for Gramalote Ridge overall and about 15 m thick above mineralization.
The silver to gold ratio is approximately 1:1.
The primary mineralization consists of pyrite and chalcopyrite. Secondary minerals include rutile and a titaniferous mineral.
Free gold occurs as argentiferous gold coeval with several tellurides and bismuth sulphosalt minerals.
Trinidad
The Trinidad deposit has dimensions of approximately 1,500 m by 500 m. Mineralization has been drill tested to a depth of about 300 m.
The Trinidad mineralization is hosted in similar rock types to those described for Gramalote Ridge.
Alteration is similar to that described for Gramalote Ridge.
Mineralized zones at Trinidad are 10–80 m thick and are continuous along strike for up to 1,500 m and down dip for >500 m. As at Gramalote Ridge, such zones periodically coalesce both along strike and down-dip. The deposit remains open at depth and along strike, especially to the west
Saprolite/saprock thickness is variable, with an average thickness of 31 m overall, and about 33 m thick over the mineralization.
Mineralization is associated with stockwork veinlets and alteration along their margins. Veinlets have been classified into seven types, and gold mineralization is associated with Type 1 (quartz with fine pyrite), Type 2 (quartz with Fe carbonate) and Type 5 (quartz with granular pyrite) veins.