High-level epithermal system. Near-surface gold & silver in jasperoids, with potential for blind polymetallic replacement mineralization.
The 6,800 hectare property is located 30km northwest of the historic Pachuca-Real del Monte mining district (Figure 1), on the western side of the Sierra Madre Oriental fold belt, within a northwest trend of historic deposits including Zimapan (Hidalgo) and La Negra (Queretaro).
Extensive mapping and sampling have defined five key drill-ready targets in the Petate West and Petate East areas.
In April 2017, Prospero secured a C$1.5-million strategic investment from Fortuna Silver Mines Inc -- a growth oriented min-tier silver and gold producer- to fund first-pass, proof of concept drilling on 3 of our key targets, including Santa Maria del Oro. Prospero anticipates drilling to begin at El Petate in September 2017.
The final permission to drill was received from the Hidalgo State branch of the Secretariat de Medio Ambiente y Recursos Naturales (“Semarnat”) in September 2017. A 1,508m, 12 hole programme testing 4 targets (Apartadero SE, Clemente, Tajo and Petate #3) was completed in December 2017, and was aimed primarily at understanding structural controls of the jasperoid bodies. Nearly all jasperoids were intersected less than 50 vertical meters below the present surface, appear to be predominantly structurally controlled, and confirmed continuity of gold values at shallow depth. Hole PET-17-05 returned 18.5 @ 0.8g/t Au from 48.6m downhole.
Future work should test the potential for structurally controlled orebodies at greater depth including blind carbonate-replacement bodies of manto and/or chimney type, containing Ag, Pb, Zn and ± Au similar to the Zimapan or Santa Eulalia polymetallic systems.
Detailed mapping of the property has identified two domains, Petate West (~5 km north-south) and Petate East (~2 km north-south), each with distinct geological and geochemical signatures. Nearly 1,200 rock chip samples have been collected to date in the two zones. Most samples are chip-grab or chip-channel samples between 1 to 1.5m long, or continuous channel samples, sampling outcrops or jasperoid boulders and fragments within float.
In the West zone, multi-gram gold assays were obtained from the the Apartadero, El Tajo and the Petate SW reefs. At Petate East, sampling returned multi-ounce silver assays. The Apartadero area (in the Petate West zone) shows stronger gold values associated with Ag-Hg-Sb-As, whereas the Petate East zone is characterized by stronger silver values in association with Au-Ba-Mn.
The presence of low temperature silica invasion and silicification, associated with elevated Hg, Sb, and As indicate that the surface exposures at Petates may correspond to the upper parts of a preserved mineralized system at depth.
The Petate mineral occurrences are hosted in the El Abra limestone of Lower Cretaceous age. These occur in a dome of the Mesozoic fold belt of the Sierra Madre Oriental. Scattered outliers of overlying andesites of the Tertiary Pachuca Group which do not host silicification suggest that the Petate hydrothermal system is more similar in age to the Zimapan skarn/replacement type deposit (~42Ma), than the age of the Pachuca vein deposit (~23 Ma).
Petate West Zone
Petate West hosts numerous silica reefs named --from north to south- La Escoba, Apartadero, El Tajo, Tecolotes, and Petate SW reef (Figures 2, 3). Some are associated with feldspar porphyry dikes with the same orientation. They feature fine crystalline to cryptocrystalline quartz as stockworks, irregular shaped breccias bodies, and veins, as well as silicification of massive limestones. In general, Petate West has higher gold than silver values.
The reefs are easy to follow at surface because of abundant float boulders and sub-outcrops. The presence of iron and manganese oxides associated with the reefs makes them easily visible on Google Earth and ASTER images.
The Plomosas mine, which exploited high grade Pb-Ag mineralization during the 1940's in the south-central zone, appears to be the south-eastern extension of the Tecolotes reef. Samples from this mine exhibit Pb values in the multi-percent range and silver values in the 30 ppm to 200 ppm range (Figure 6).
This target features jasperoid outcrops and float over an area of 1.3km by 200m. It yielded the highest overall gold geochemistry in the Petate claims. Highlights (Figure 5) include:
Trenching and detailed sampling in the Apartadero Central area defined a number of targets including jasperoid breccias with gold values ranging from 1.0 ppm to 5.6 ppm, and a structurally controlled vein target anomalous in silver with values ranging 2.8 to 31.4 ppm (Figure 7). Several jasperoid breccias bodies at Apartadero SE show anomalous gold with values ranging from 1.0 to 6.6 ppm Au.
El Tajo Target
This zone shows intense silica flooding and abundant float of brecciated jasperoid over 500 meters by 150 meters. Anomalous gold values range from 0.1 ppm to 2.4 ppm, distributed in a half moon configuration and at lower elevations at the northwest end of the El Tajo ridge and target zone (Figure 4).
The plan view dimensions of both the Apartadero Central-Apartadero SE, and El Tajo target (500 to 600 metres in length, and 150 to 200 meters wide), and presence of widespread fractions of ppm to multi-ppm Au, indicate there is potential for open pit mineralization in both target zones.
Petate SW Reef
This is a tabular silicified reef which outcrops for 1.2 km along a >3 km long regional-scale range-boundary fault on the southern boundary of an uplifted window of Cretaceous folded sediments (Figure 2). To the northwest it trends under post-silicification Pachuca Group andesite cover. The reef is anomalous in gold (up to 3.6 ppm), silver (38.9 ppm), Hg (up to 36.4 ppm) Sb (up to 3,690 ppm), As (up to 10,000 ppm), Pb (up to 3,310 ppm), and Zn (up to 6,400 ppm).
Petate East Zone
The Petate East zone is made up of four silica bodies named Petate #1 to Petate #4, all of which occur along a strike length of 2.5km. In contrast to the anomalous gold geochemistry at Apartadero, the Petate East geochemistry shows higher silver levels, particularly in the eastern zone, (Petate # 1, #2, and #3 targets) with silver assays commonly above 25 ppm and up to 140 ppm (Figure 5). Soil sampling indicates that the Petate #1, and Petate # 2 anomalies are open to the west.
The Petate East zone also shows elevated iron and manganese geochemistry with anomalous values up to double digit percent range. The historic "El Aguila" mine at the southern extension extracted manganese-rich ore from a gossan at the contact with a feldspar porphyry dike (Figure 3). Two samples from the gossan assayed 345 ppm and 595 ppm silver (Figure 5), highlighting the presence of high grade silver associated with manganese oxides.
This target is exposed in several outcrops along a small creek for a distance of 50m. Thirteen channel samples returned consistent gold values averaging 0.166 ppm Au (with a high of 0.49 ppm), and 10.4 ppm silver (with a high of 89.4 ppm). Soil sampling shows that the Petate #3 target area extends further to the northwest. A subdued gold anomaly extends an additional 400m to the northwest which is also reflected in mercury and iron geochemistry.
Petate East Soil Sampling
487 soil samples were collected from a grid over the Petate East zone (see news release of Jan 28, 2013). Silver anomalies greater than 5 ppm and up to 52.3 ppm are prominent in the Petate #1 and #2 target areas. The anomalies are open to the west particularly in the western (hangingwall side) of the Petate #2 target where the highest silver values (52.3 ppm, 37.4 ppm, and 19.9 ppm) were obtained (Figure 8).
Prospero completed a limited 12 hole first-pass drill program in December 2017. Cross sections for all holes are thumbnailed on the left hand side of this page together with a full table of anomalous intercepts, collar positions and azimuths.
Drilled on section line G-G' to test beneath extensive outcrops of jasperoids at the El Tajo zone, PET-17-05 is mineralized over most of its 67m length. Highly encouraging gold grades were cut over 3 separate intervals (18.3m, 12.2m and 18.5m intervals respectively), with grades increasing downhole. Difficult drilling conditions with broken jasperoidal ground and poor recoveries forced the abandonment of the hole at a final depth of 67.1m. The highest grades are associated with intervals of black jasperoidal breccias. Hole PET-17-06 was subsequently drilled from the same collar location with the same azimuth but at a dip of 55 degrees as a redrill of 05. Key weighted average intervals from hole 05 are:
|From (m)||To (m)||Interval (m)||Au g/t||Ag g/t|
Hole PET-17-06 drilled into the El Tajo target beneath and parallel to hole 17-05 with an azimuth of •325°. (Hole 17-05 returned a best interval of 18.5m@ 0.8g/t Au + 5.0 g/t Ag with poor recoveries) Hole 17-06 was stopped at 165.6m and cut multiple mineralized zones including:
|From (m)||To (m)||Interval (m)||Au g/t||Ag g/t||Zn %|
From surface to 14.7m the hole cut alluvium with clasts of jasperoid and andesites. The gold-bearing intervals from 44m to 54m and from 60.3m to 63.5m are hosted in fragmented black jasperoid after limestone, and correspond to the 18.5m @ 0.8g/t Au reported for hole PET-17-05. From 63.5m to the end of hole, 17-06 cut fresh dolomitized limestones.
Holes 17-07 and -08 were drilled from the same collar position as hole 17-06, but on a section line oriented roughly northeast-southwest. (Hole 17-07 azimuth roughly SW, 17-08 azimuth to the northeast). The hole cut reddish muddy alluvium with local jasper fragments from surface to 31.6m. From 31.6m to the end of hole at 93.2m it cut limestone with a jasperoidal zone from 48.9m to 54.4m. Interestingly it returned anomalous gold mineralization for much of its length as follows:
|From (m)||To (m)||Interval (m)||Au g/t||Ag g/t|
Hole 17-08 was drilled from the same collar position as hole 17-07. It ended at 165.2m in fresh limestone. The hole returned 2 anomalous gold intersections with a best of 11.8m @ 0.15g/t Au from 13.3m downhole hosted by a zone of jasperoidal breccia with silica-calcite veining. A second jasoperoid from 53.8m downhole returned 7.3m @ 0.14g/t Au + 11.5g/t Ag. Both zones appear to be steeply dipping and possibly correlate with surface outcrops of jasperoid.
Apartadero SE Target
PET-17-01 was stopped at 178.9m. Gold-mineralized jasperoid zone was intersected over a 3.4m interval from 81.85m to 85.25m which returned 3.5g/t Au, although core recoveries at (32%) were low due to the presence of voids, not bad ground. The jasperoid is similar to a zone mapped at surface which may be its upward projection. From 124.5m to 151.8m (27.3m) the hole intersected calcite-veined, brecciated, and variably decalcified limestone. One sample returned a weak gold anomaly (0.18ppm) in this zone.
It now appears that the hole was drilled in the hanging wall or footwall of a jaseroidal structure and parallel to it rather than perpendicular to its strike. Three additional holes were drilled at the Apartadero SE target from north to south (PET-17-09), and from south to north (PET-17-11 and PET-17-12) in order to test for the presence of an east-west structural control for the Apartadero SE jasperoids.
Hole 17-09 was drilled across the trace of hole PET-10-01 roughly from north to south to investigate the intersection of 3.4m @ 3.5g/t Au noted from 81.9 to 85.3m in hole PET-17-01 (see news release dated November 8, 2017). The hole cut multiple gold-bearing zones as follows:
|From (m)||To (m)||Interval (m)||Au g/t||Ag g/t|
The intercept from 43.8m appears to be the zone seen in hole 17-01 albeit deeper in the section, suggesting a steep dip to the zone. The highest grade in hole 17-09 was from a 40cm sample which returned 3.5g/t Au from 43.8m downhole. The zone has now been traced for 50m vertically below where hole 17-01 cut it.
Hole 17-11 was drilled from a collar roughly 150m south of 17-09 with an azimuth approximately due north again investigate the intersection of 3.4m @ 3.5g/t Au noted in hole PET-17-01. The hole appears to have cut the same zone from roughly 26.7m to 42.7m downhole, returning 16m @ 0.75 g/t Au and 2g/t Ag (see cross section).
Hole 17-12 was the last hole drilled in the current program at Petate from a collar roughly 50m south of hole 17-11, with an azimuth north-northeast to test beneath the intercept reported above for hole 17-11. The hole was stopped at 216.2m in limestone after cutting 3 jasperoid zones. Prospero's geologists believe the zone in hole 11 was cut between 66m to 69.9m downhole implying its dip has flattened. This zone returned 3.9m @ 1.2 g/t Au + 3.7 g/t Ag. A second zone from 176.5m downhole returned 4.4m @ 13.6 g/t Ag with trace anomalous gold.
Apartadero Central Target
PET-17-02 was drilled due north under the Apartadero Central target to test for its down dip extension. The best candidate to represent the Apartadero Central zone is a brecciated interval from 22.40 to 30.35 meters which hosts grey silicified limestone fragments supported in a soft orange reddish matrix. Only one sample (W680086) returned weakly anomalous gold (0.13 ppm Au over 1.5m).
PET-17-03, which was stopped at 63.5m depth, was drilled along the same section as PET-17-02 but from north to south and returned no significant results. The purpose of this hole was to clarify if all the brecciated zones of PET-17-01 are related to manto-like sub-horizontal zones or are related to steeper northwest-southeast striking structures. The hole cut fresh limestone with calcite veinlets and stockworks, and no brecciation suggesting the later case is more likely. It is considered likely that hole PET-17-03 was drilled entirely in the footwall of the Apartadero Central occurrence.
Hole 04, drilled to a final depth of 113m, was collared to test the Apartadero Central target from east to west. The hole cut fossiliferous limestones with local calcite veining, and is also suspected to have drilled the footwall of the Apartadero Central target. No significant assays were received.
Fluid inclusion results obtained from quartz samples from Petates indicate that the fluids associated with deposition of the quartz were relatively low temperature and salinity (130°C to 230°C; 0-3.0 wt.% NaCl equiv). This in turn suggests that the surface exposures in the project area correspond to the upper parts of a preserved mineralized system at depth.
Additionally, the geochemical signature of the Petate West zone (Au-Ag-Hg-Sb-As) indicates a low-sulfidation system. The Petate East zone geochemistry (Ag-Au-Ba-Fe-Mn) is more indicative of intermediate sulfidation hydrothermalism.
With first-pass drilling of 12 holes completed, Prospero is evaluating the results to identify deeper targets for possible drill testing with its partner, Fortuna.
Future work should test for the continuity at depth of the structurally controlled jasperoids, as well as for blind carbonate-replacement bodies of manto and/or chimney type, containing Ag, Pb, Zn and ± Au similar to the Zimapan or Santa Eulalia polymetallic systems. In this model, copper may become more enriched at depth as the skarn environment is approached. Jasperoid with comparable silver-rich manganese oxides is seen in the shallow portions of Santa Eulalia and other similar deposits, above the principal silver-zinc, and lead-rich, carbonate-replacement chimneys and mantos.