Summary:
Deposit types
Marmato is interpreted to be a porphyry hosted gold deposit with shallow epithermal and deeper mesothermal features and this interpretation has informed the exploration and mining plans.
The Upper Mine is distinguished by a sulfide rich, structurally controlled system of veins and veinlets of pyrite, arsenopyrite, iron-rich sphalerite, pyrrhotite, chalcopyrite, and electrum veins associated with biotite, sodic-calcic, and epidote-chlorite-carbonate alteration.
Mineralization
Marmato mainly comprises northwest and west-northwest trending veins and veinlets, with intermediate sulfidation epithermal and mesothermal mineralization styles transitioning with depth from the Upper to the Lower Mines. The veins outcrop at the surface, and within Aris Mining’s mining titles, mineralization extends vertically over 1,100 m and remains open at depth and along strike, and has a high expansion potential from future underground drilling programs.
The Upper Mine mineralization is characterized by epithermal mineralization comprising wider, parallel, sheeted, and anastomosing sulfide rich veins and veinlets with minor quartz, carbonate, pyrite, arsenopyrite, iron rich sphalerite, pyrrhotite, chalcopyrite, and electrum. Broad zones of intense veinlet mineralization hosted within a lower grade auriferous porphyry stock are locally referred to as “porphyry pockets” or “porphyry” mineralization.
In the Upper Mine, interpretations of 94 different veins and 53 zones of disseminated mineralization occurring directly in the hangingwall and footwall of the veins, and 89 discontinuous “splay” veins have been created for the mineral resource estimate. The mineral resource estimate of the porphyry “pocket” style mineralization has been undertaken using a grade indicator approach. The currently defined footprint of mineralization at the Upper Mine covers over 1,000 m east-west x 1,500 m north-south, and extends vertically for 350 m.
Marmato Porphyry
Suite The P1 intrusion is the main dacite unit of the Marmato Porphyry Suite and comprises by far the largest volume of mineralized rock at the Property. It is overlain by quartz-sericite-graphite shales of the Arquia Complex, and contains small intrusions of the P4 andesite as well as the other porphyry intrusive bodies. The P1 dacite porphyry is a compact, granular rock characterized by large (5 millimetre, mm) quartz phenocrysts, hornblende, biotite, and plagioclase phenocrysts zoned with a fine granular matrix of quartz and plagioclases, with variable sizes and percentages.
The P2 porphyritic dacite intrusion is smaller than P1 and P4, and has only been observed in drill core. It is a hypocrystalline rock with medium grain size (finer than P1), light gray coloration, comprised of small sub-rounded quartz crystals accompanied by slightly zoned and epidotic plagioclase phenocrysts, biotite, and euhedral and chloritized amphiboles.
The P3 porphyritic andesite dikes have a northwest and east-west trend and are in contact with P1 in the Cascabel gorge and in Echandia, and also crosscut P1 and P2. They have slightly zoned euhedral plagioclase megacrystals with small subhedral crystals of plagioclase, biotite, hornblende, and lesser quartz and magnetite.
The P4 andesitic porphyry trends northeast, is approximately 1,600 m long x 750 m wide, forms a stock on the northwest side of Cerro Los Novios, and extends northeast through Echandia. Towards the southeast there are numerous P4 dikes with a northwest and east-west trend. It cross cuts P1, P2, and P3. The intrusions are grayish, massive, slightly equigranular, with scarce to no quartz, with abundant phenocrysts of coarse plagioclase with biotite, hornblende, and magnetite, with chlorite amphiboles.
The P5 porphyritic dacite intrusion cuts P1 in the Cascabel gorge and elsewhere. It has a massive, uneven, hypocrystalline texture, with small euhedral crystals of quartz and elongated plagioclase phenocrystals up to 10 mm in length, with biotite and hornblende crystals. P5 does not host mineralization.