Summary:
At the Hemco Property, the majority of mineralization consists of volcanic hosted gold-silver + copper, lead, and zinc epithermal quartz veins of intermediate sulphidation type. Three groups of mineralized, northeast trending veins, called the Panama Group, Pioneer Group, and Constancia Group, respectively, occur within andesitic and agglomerate units. Each group hosts up to 70 principal veins or vein segments, which collectively define a 20 km long mineralized corridor and host the Panama gold and Pioneer gold and silver deposits. The Porvenir polymetallic deposit is hosted within adjacent volcanic rocks.
Two systems characterize the Panama deposit. A set of northeast trending veins, which are often truncated by northwest-trending structures, and a set of northwest trending veins. In general, veins within the Panama deposit consists of veins that are lensoidal to tabular in shape, and pinch and swell along strike and dip. The northeast set of veins generally dip to the northwest from 50-80°, with a strike length of less than 0.5 km to greater than 3.0 km and range in thickness from less than 0.05 m to greater than 20 m. Northwest trending veins dip either to the northeast or southwest from 60-80° and can extend greater than 3 km along strike, with a thickness ranging from less than 0.1 m to approximately 7.0 m.
The Pioneer deposit consists of four mineralized veins that are spread over a strike length of approximately 1,900 m and have a maximum depth of 250 m below surface. These veins have a northeast 45°-50° southwest striking orientation and dip to the northwest from 50°-80° with a thickness ranging from 0.5 to 6.0 m.
The Porvenir deposit consists of polymetallic mineralized veins that are spread over a strike length of approximately 2,200 m and have a maximum depth of 400 m below surface. These veins have a northeast 55°- 65° southwest striking orientation and dip to the northwest from 50°-80° with a thickness ranging from 0.8 to 16.0 m.
The Luna Roja Deposit is hosted within skarns associated primarily with the selective replacement of carbonate rocks of the Cretaceous Metapán Formation. The Luna Roja Deposit mineralization is hosted in red-brown-yellow garnet, magnetite and hematite skarn, green-yellow garnet-pyroxene skarn. Bleached or gray marble and hornfels also occur in the Luna Roja Deposit and several intrusive phases have been delineated. An approximately 450 m long by 80 m wide by 250 m deep mineralized ore shoot was delineated in this main part of the Luna Roja Deposit, which is open laterally toward the southeast and to depth.
Vein Deposits
The majority of mineralization within the concession area consists of volcanic hosted gold-silver ± copper, lead, and zinc epithermal quartz veins of intermediate sulphidation type. There is a vertical zonation of metals, and base metal contents are higher at depth, although, in general, gold grades appear to stay constant except in those areas near surface where residual gold has been liberated by the oxidation of pyrite and weathering/disintegration of host rock.
The epithermal veins at Bonanza are characterized by moderate to intense propylitic alteration of the andesite wall rocks locally accompanied by argillic alteration and silicification. There are several variations in style of mineralization among the veins.
Veins in the southwest part of the district are characterized by gold mineralization associated with quartz, chalcopyrite, and hematite enriched in base metal sulphides. Gold mineralization in veins toward the northeast, i.e., the Pioneer and Panama groups, is associated with quartz and chlorite and generally lower base metals content. The difference in gold and base metal tenor between the Panama, Pioneer, and Constancia groups may be a function of the spatial relation with the intrusive heat source. Shallow epithermal veins are characterized by low grades but wider zones resulting from bifurcations and quartz stockwork zones. Base metal contents are generally lower at the shallow depths than what has been encountered in deeper parts of the system and trace elements such as strontium and barium are higher. Alteration is characterized by zonation from propylitization of country rocks to argillic alteration as the vein is approached. Silicification can be widespread and intense. Phreatic breccias are common as are boiling textures such as bladed quartz after calcite. Deeper portions of epithermal systems are typically enriched in base metals and have higher gold grades. The veins are more discrete, and alteration is characterized by moderate to strong propylitization of the wall rocks. In the Bonanza district, all of the veins are interpreted to lie in the middle to deeper levels of an epithermal system. On the basis of base metal content, the Porvenir, Leticia and San Antonio veins in the Constancia Group are interpreted to be deeper relative to the Pioneer and Panama groups.
Byington (1996) noted that quartz veins are controlled by strike-slip faulting with both sinistral and dextral displacement and mineralized shoots are controlled by gold deposition introduced during dextral strikeslip movement resulting from wrench tectonics. Gold grades are higher in areas of increased fracture density and permeability such as flexures in strike and dip. This may also account for the observed periodicity of mineralized shoots and non-mineralized portions of the structures. In a very general sense northwest dipping mineralized shoots more often have southwest plunges and southeast dipping shoots have a vertical to steep northeast plunge.
The Bonanza epithermal gold mineralization may be related to a 40 km diameter pluton on the southeast side modeled from pseudo-gravity high. The Siuna and Rosita copper-gold deposits are also on the edges of this interpreted pluton. Recent petrographic studies by Miller (2016) of the Tesoro, Cruzada, and Northeast vein systems concluded that the three epithermal systems record hydrothermal events with similar silicate-sulphide assemblages. A paragenetic sequence was established that can be used as a working model for identifying textures and timing within the complex vein networks. The study documented four textural stages of quartz vein filling termed Q1 to Q4 and corresponding sulphide assemblages termed S1 to S4 which are combined as Q1/S1 to identify the earliest quartz-sulphide event and similarly for younger vein episodes.
Skarn Deposits
The Luna Roja deposit is hosted within skarns associated primarily with selective replacement of carbonate rocks of the Cretaceous Metapán Formation. The Luna Roja skarn shows prograde and retrograde calc-silicate alteration, hosted mostly in carbonate rocks, which led to the formation of redbrown- yellow garnet, green-yellow garnet-pyroxene, and wollastonite.
The skarn in Luna Roja shows different types according to its mineral assemblage and colour: a) a yellowbrown skarn which consists of brown-yellow medium-coarse size grained garnet, with poor presence or absent pyroxene; b) a dark green skarn with pyroxenes with a ratio of 3:1 over garnets, accompanied by amphibole and magnetite; c) a yellow-green skarn, where garnets of this colour are predominant over pyroxenes in a ratio of 6:1 to 9:1; d) a red-brown skarn, which can be found adjacent to igneous subvolcanic bodies, as alteration in veins, layers and patches of red and brown garnet.
Also, a structurally controlled late mineralization system, placed in subvertical structures which are possibly related to northwest regional faulting, is overprinting the skarn deposit. The most important unit of this system consists of a red quartz-calcite hydrothermal breccia, ± hematite ± magnetite ± adularia ± pyrite ± chlorite. The host rock of this system was affected by these oxidized fluids, hence the marble and skarns adjacent show red patches. The nature and timing of this event has not been determined yet.
Production
Historically, ore purchased from artisanal mining cooperatives formed 40% to 50% of the ore processed by the Hemco Plant and 100% of the ore processed by the smaller Vesmisa Plant and La Curva Plant. In 2023, the processing plants at the Hemco Property processed a total of 417.34 kt of ore purchased from artisanal mining cooperatives, including 345.11 kt (83%) of the ore processed at the Hemco Plant, and 72.23 (17%) of the ore processed at the Vesmisa Plant and La Curva Plant. Production from ore purchased from artisanal miners was 93.2 koz Au, representing 74% of the Hemco Property’s 126.0 koz Au aggregate production in 2023.
| Commodity | Units | 2024 | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
|
Gold
|
oz
| ....  | .... | .... | .... | .... | 125,206 | 106,942 | 104,001 | 79,481 | 69,308 |
|
Silver
|
oz
| | .... | .... | .... | .... | | | | | |
All production numbers are expressed as metal in doré.
^ Guidance / Forecast.