A sample of mineralized rock from the Shimpia target showing galena – the silver-coloured mineral – with brown sphalerite (zinc-bearing mineral) and the whitish mineral is quartz and barite, the barium-bearing mineral.
Aurania has discovered a 15km long trend in which silver-zinc-lead-barium occurs – the Shimpia targeta area, that is enclosed by the various Tiria epithermal gold-silver targets.
Silver-zinc-lead deposits of significant size are not known from Ecuador, but large deposits do occur in the Bongara and San Vicente mineral provinces of adjacent Peru. In fact, the Shimpia target in Aurania’s Lost Cities Project is in the same layered, sedimentary sequence as the deposits in Peru, so discovering the Shimpia target was not all that surprising.
Silver is usually located in the main lead-bearing mineral, galena. Galena usually forms perfectly square crystals, and a field guide is that the more curved the edges of the square crystals, the more silver the galena contains. These deposits are usually found where faults cut through limestone layers, and they usually contain barium, a very heavy mineral that has abundant industrial uses. Barium can provide a useful revenue stream that augments income from silver, zinc and lead.
Aurania’s ‘Shimpia’ target lies in the vicinity of a fault zone that extends from a large magnetic feature that is interpreted to be a porphyry. Aurania’s current exploration model has the mineralization linked to that porphyry using the concept illustrated in the graphic below that was developed for the Glover porphyry and associated carbonate-replacement silver-lead-zinc in limestones layers. This exploration model will undoubtedly evolve as more information becomes available to us.
These Carbonate Replacement Deposits (CRDs) are genetically related to intrusive magma bodies that provided heat and metal-bearing fluids into the mineralizing system. They are termed “replacement” because the mineralization replaces the limestone as it is dissolved by the mineralizing fluids passing through limestone. The fluids typically alter the limestone to dolomite, a magnesium-bearing carbonate. These deposits tend to grade from copper-rich areas close to the porphyry, through copper-zinc-silver, lead-silver, manganese-silver, and ultimately, on the coolest, fringes of the mineralized system, to manganese and ultimately mercury-bearing zones. The zinc-lead silver zones can lie within the sedimentary layering, in which case they are called mantos, or cross-cutting to the layering, in which case they are called chimneys.
Typical metal zoning in a limestone adjacent to a porphyry. Carbonate Replacement Deposits change gradually from copper-rich, to zinc-rich, to lead-rich with greater distance from the core intrusive magma area, which may be a mineralized copper porphyry in some cases. Graphic is from Simpson, 2018.
