Summary:
The 3,019 hectares property covers extensive carbonate replacement deposit-type zinc-lead-silver mantos (beds).
Plomosas is located in a historic zinc-lead-silver mining district, with mineralisation hosted by a Palaeozoic sequence of shales, argillaceous limestones, reefal limestones, ‘conglomeratic’ limestones and sandstones. This approximately 1,600 metres-thick carbonate-rich sequence forms part of the Ouachita “Geosyncline”, which was inverted in a thrust deformation phase during the Upper Palaeozoic Appalachian Orogeny.
Characteristics of the deposit lead to the classification as an IRT III type mineralisation (Intrusive Related type III deposit) but may have some distal style affinities.
The control on mineralisation is both lithological and structural, but local structural bending of the manto is very important as it is strongly folded in a relatively regular pattern, oriented north/northwest to west/north-west striking. The segment of the fossiliferous horizon with the best potential is north/north-west striking with a south-east plunge. The N/NW orientation of sections of the stratigraphy (due to folding) is considered important in localising mineralisation.
Mineralisation in the Plomosas district exists as stratiform sheets of manto-style mineralisation with crosscutting “chimneys” influenced by the location of cross-cutting linking faults. The host rocks are predominantly limestone and shale with marbles present in areas including the hanging wall sequence. The hanging wall to the mineralisation is constrained by a zone of ductile-brittle deformation that is part of a larger ‘horst’ structure where a series of normal faults crosscut a sequence of folds and thrusts. This system of brittle deformation is evident along a series of normal sub vertical faults generally striking NW-SE.
At Plomosas, the average thickness of the manto-style mineralisation is around 3m within a thicker sequence up to 25m thick containing limestone + shale + marble that dips shallowly (10° – 40°) to the north east. Mining has extensively focused on the limestone units and shown the ore to be highly visible with sharp contacts.
The mineralogy is simple, consisting of iron-poor sphalerite, galena, silver, pyrite, chalcopyrite, barite, and calcite. The ore bodies are hosted by shale and marble on the footwall and hanging-wall respectively. Intense marblisation is restricted to a few meters from the hanging wall contact.
Level 7
Mineralisation in the Level 7 SOX is structurally controlled with a plunge component of approximately 20o - 30o to the southeast along a shallow dipping plane defined by the Mina Vieja Manto unit. Economic mineralisation in this system is coincident with flexures that host the thicker, high grade mineralisation.
The Level 7 Resource represents sulphide mineralisation that has been affected by late-stage oxidation by oxygenated water flowing through localised faulting. This manto-style sulphide mineralisation is present as ‘kernels’ within rinds of oxidised sulphides which can require a different metallurgical process to that of pure fresh sulphides as found in the Tres Amigos Resource.
Structural mapping at the Level 7 SOX has confirmed that these northeast faults have moved and jostled ore blocks up and down along the strike direction, making extraction of ore a challenging exercise. The relative movement of these blocks is no more than three to four metres in the vertical direction.
The shallow dipping (10°-40°) Plomosas mineralisaon has been mined in several stages since 1943 down to approximately 270m below surface via room and pillar stopes using tradional jack leg drill and blast techniques. The mineralisaon is open at depth and there is more than 6km strike of prospecve stragraphic horizon and mineral prospects on the property, providing for significant addional exploraon potenal and drill targeng. Impact Silver is currently drilling near mine targets to define and expand resources for mining.
Dimensions
The Tres Amigos Mineral Resource area extends over a southeast-northwest strike length of 320m (from 3,216,570mN – 3,216,740mN), has a maximum width of 190m (476,080mE – 476,250mE) and includes the 200m vertical interval from 1,090mRL to 890mRL.
The Level 7 Mineral Resource area extends over a south-southeast – north-northwest strike length of 400m (from 3,216,930mN – 3,217,300mN), has a maximum width of 110m (476,230mE – 476,340mE) and includes the 90m vertical interval from 950mRL to 860mRL.