Summary:
Gold mineralization at Segovia occurs in mesothermal quartz-sulfide veins hosted by a batholith. They have been classified as “Oxidized Pluton-Related Gold Deposits” (Sillitoe, 2008), are thought to have formed after the cooling of the batholith and may have a genetic relationship with the batholith as well as with the regional stress regime related to the Otú fault.
Gold mineralization at Segovia occurs in mesothermal quartz-sulfidic veins hosted by diorite to granodiorite rocks of the Segovia Batholith. The well-known, partially exploited veins dip at approximately 30° to the east or north-east. There are also a number of steeply dipping shear-zones hosting quartz veins with a N40W trend in the western part of the concession, termed the Las Verticales Veins System.
In general, the veins are formed of quartz with minor calcite and coarse-grained sulfides comprising pyrite, galena and sphalerite, and typically show a close spatial relationship with lamprophyre to adakite dykes. Gold and electrum occur as fine grains (<20 microns) and visible gold is generally common in the high-grade shoot sectors of the mines. Native silver has been reported. The wallrock alteration to the veins affects the basalt dykes and the granodiorite in a narrow zone a few meters wide with potassic (biotite), argillic (illite) and propylitic alteration most commonly encountered along with selective mineral replacement by chlorite, epidote, pyrite and calcite.
Gold mineralization is hosted by a series of quartz-sulfide veins. The main sulfides present are pyrite, chalcopyrite, sphalerite, and galena with higher grades seemingly related to high proportions of the latter two. The veins themselves exhibit three main trends:
- N-S to NE strike, with a dip of 30° E;
- E-W to NW strike, with a dip 30° to N or NE; and
- NW strike, with a dip of 65-85° NE. These occur on the west side parallel to a NW -trending segment of the Otú Fault.
The low angle veins have formed along thrust faults. These often have thrust duplex structures, resulting in pinching and swelling of the veins; these is no evidence to suggest any systematic change in grade through these pinch and swell structures. The average width of the quartz veins is 0.95 m, with a maximum width of up to 9.00 m. On occasion, a clear intersection lineation can be observed in the veins plunging toward 060°, sub-parallel to the plunging high-grade mineralization observed in the Mineral Resource modeling suggesting the importance of cross cutting structures.
The quartz veins commonly follow dykes or sills with a width of about 2 to 3 m. These dykes can be found in the hanging-wall or the footwall material, both, or in the middle of the mineralized vein. The lamprophyre dykes have very fine phenocrysts of white plagioclase in a fine grained, dark- colored matrix, whereas the adakite dikes show coarse phenocrysts (7 mm) of white plagioclase in a fine grained, light-colored matrix.
There is always a close spatial relationship between the veins and dykes, and the dykes are used as a guide to mineralized structures during exploration drilling or drifting.
The veins are offset vertically by more than 50 m by high angle faults which show a reverse sense of displacement. The principal fault trends are NE with dip of 65° to 85° NW, and NW with dip of 85° W to 65° E.
Production
In addition to the material produced from the operating mines, Segovia also processes material from small-scale contract miners. In 2022, ore processed from Company-operated mines was 502,868 t and Contractor-operated mines was 108,898 t.
| Commodity | Product | Units | 2023 | 2022 | 2021 | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
|
Gold
|
Metal in doré
|
oz
| ....  | .... | .... | .... | 214,241 | 193,050 | 148,659 | 126,261 | 92,894 |
|
Silver
|
Metal in doré
|
oz
| | | .... | .... | 187,820 | 160,954 | | 125,639 | 99,236 |
|
Zinc
|
Metal in concentrate
|
lbs
| | | .... | | | | | | |
|
Lead
|
Metal in concentrate
|
lbs
| | | .... | | | | | | |