Gold and Silver


Low Sulphidatio Epithermal Au-Ag Rhyolite Flow Dome Complex

Type of Deposit

Fronteras, Sonora



Surface Area

Cecilia Project

COMMODITY: Gold and Silver
DEPOSIT TYPE: Low Sulphidation Epithermal Au-Ag Rhyolite Flow Dome ComplexLOCATION: Sonora, Mexico
SIZE: 6,897.3075 has
STATUS: Drill Permitted, Available for Option


The Cecilia project is located 40 km southwest of the Mexico-U.S.A. border town of Agua Prieta and is easily accessed by paved a highway and dirt roads. The property covers 6,897 ha. within the municipality of Fronteras, State of Sonora, Mexico.  The world-class open-pit Cananea porphyry copper mine is situated 48 km west-southwest of Cecilia.  Deposit analogs for Cecilia include the La Pitarrilla deposit in Durango which contains 526 million oz Ag (Measured + Indicated, SSRI website) and Fresnillo’s San Julian silver mine containing over 230 million ounces Ag.


As many as 30 abandoned exploration adits, several small underground galleries and surface prospect pits are distributed over the upper slopes of Cerro Magallanes and are believed to date back to the 1910’s and 1920’s. 

Around 1981, the Consejo de Recursos Minerales (CRM) initiated exploration at Cerro Magallanes.  Over a 3-year period CRM carried out a comprehensive exploration program, including:

  • 896 km2 squared of regional mapping
  • 635 surface rock chip samples
  • 14.3 line kilometres of induced polarization
  • 1,412 m of underground mapping
  • drilling of 4 diamond drill holes totalling 732.3 m

In April of 1994, Cambior Exploracíon S.A. de C.V. entered into an option-to-purchase agreement with the DGM for the project. The work under the agreement by Cambior is summarized below: 

  • 9 km2 1:2,500 orthophoto and topo map with 5 m contours
  • 6 km2 of geological mapping at 1:2,500
  • 12.85 line kilometres of induced polarization, ground magnetic survey over 2.8 km x 2.4 km
  • 666 surface rock chip samples
  • 1,200 m of underground mapping, 388 underground rock chip samples
  • drilling of 19 diamond drill holes totalling 3,817.6 m

Minerales El Prado S.A. de C.V. (“El Prado”), the Mexican subsidiary of Chesapeake Gold Corp., was the next company to acquire the project.  El Prado collected a total of 738 surface rock chip samples between 2004 and 2009.  From 2009 until 2013 essentially no work was done.

In January of 2017, Riverside Resources Inc. purchased the Violeta concession from Millrock Resources Inc. subject to a 0.5% Net Smelter Return royalty. Riverside has signed an option to purchase agreement with Gunpoint Exploration Ltd. (the underlying holder of the project) to acquire a 100% interest in the three Cecilia-Margarita concessions by making cash payments and share issuances over a four-year period.

The Cecilia-Margarita concessions are subject to a 1% NSR royalty in favour of the Servicio Geologico Mexicano (formerly Consejo de Recursos Minerales).

During 2017, Riverside completed a work program of rock-chip sampling that was designed to primarily confirm the existence of the more intensely mineralized gold occurrences found on Cerro Magallanes.  The sampling work was done within an area of roughly 1 kilometer by 200 meters at the core of the project area and mainly on the eastern and northeastern slopes of Cerro Magallanes. This work confirmed the past work and outlined a main area for follow-up exploration


The Cecilia project is centered on a large middle Tertiary age (Oligocene) rhyolite flow-dome complex that forms the prominent topographic feature of Cerro Magallanes.  The dome complex intrudes and unconformably overlies a sequence of marine clastic sedimentary rocks of the middle Cretaceous Cabullona Group. The upper portion of the flow-dome complex is composed of a mixture of quartz-feldspar, massive, flow-brecciated and banded porphyritic rhyolite.  The lower portion of the complex as determined by drill-hole logs is dominated by a thick unit of rhyolite lithic tuff, tuff-breccia and clastic sedimentary rock fragments supported by a tuffaceous, rhyolitic groundmass.  Irregular bodies of talus-breccia exist as a litho-facies within the pyroclastic units. 

Gold mineralization is concentrated within an area 1,000 meters in width (east-west) by 200 meters north-south, with the peak of Cerro Magallanes being at the western end of this zone. Multi-element geochemical data shows that gold is inconsistently associated with anomalous concentrations of Ag, Mo and Pb.  The correlation coefficient for the element pair Mo:Pb is 0.942, whereas the correlation coefficients for Au:Ag, Au:Mo and Au:Pb are only 0.274, 0.248 and 0.089, respectively.  Significant concentrations of silver occur at lower elevations in the flow-dome complex at the eastern limits of the 1,000 m by 200 m zone of mineralization that has been defined at Cecilia.  

West Target Area

The main Cerro Magallanes peak occurs along a northwesterly trending ridge line that extends to the peak of Cerro Magallanes.  Riverside collected 45 rock-chip samples on the West Target with the highest gold assay obtained being 2.69 g/t Au. Gold in these samples is noted as being very finely disseminated in quartz-iron oxide (hematite-goethite) stringers and veinlets as well as in dikelets and irregularly shaped zones of brecciation in the flow-dome rocks along the ridge. Trace elements showing slight enrichments in the auriferous samples are Mo, As and Sb.  

A 90m-long adit with three levels of small galleries (totaling 184 meters) exists in the central part of the target area.  Identified as Obra-26, these working’s ‘galleries’ are aligned NW-SE, apparently following a mineralized structure with this orientation. Cambior’s sampling (1994?) produced 32 chip-channel samples with gold ranging from 0.2 to 4.76 g/t Au, with 14 of these samples assaying greater than 1.3 g/t gold.  The working was developed in moderately to highly fractured rhyolite porphyry bedrock containing abundant disseminated and fracture-controlled hematite along with veinlets of quartz and fluorite.  Hematite appears to be partially derived from the oxidation of disseminated pyrite.  No drilling has been conducted in this West Target area; a high priority target for Riverside. 

North Breccia Target Area

The North Breccia target area is located on the northeastern slope of Cerro Magallanes and shows as a prominent zone of iron oxide staining which has returned some of the most extensive gold mineralization on the project.  The target area has an outline of about 250 m by 100 meters and is marked by multiple zones of hematite stained hydrothermal brecciation, locally with open-space crystallization of colourless quartz and purplish to colourless fluorite. Quartz ± fluorite veinlets and stringers are also common.  Alteration consists of widespread disseminated and fracture-controlled hematite and hematite clay-rich gouge material which is found in a number of mainly NW-SE trending minor faults.  Of the 21 rock-chip samples collected by Riverside, 18 samples returned gold assays ranging from 0.48 to 7.46 g/t Au.  Gold is the only trace element that is noticeably enriched in the mineralized rocks.  

CRM tested this prospect in 1983 with drill hole DDH-83-03 and appears to have passed through strongly fractured and faulted flow-dome lithologies that display structurally controlled silica and chlorite alteration.  The geological drill log shows it passed through variably silicified and chloritized porphyritic rhyolite for approximately 135 m, then through chloritized and intensely fractured banded rhyolite for 30 m, and at a down-hole depth of 195 m it entered rhyolite lithic tuff. Core samples were apparently collected for the entire length of the borehole but the assaying method that was performed on these samples was quite rudimentary and as a result are unreliable.

Cambior tested this area in 1995 by four drill holes. The best drill-hole intersection of gold mineralization was obtained in hole 138-95-08 that averaged 1.41 g/t Au over 30.0 m, beginning at 4.0 meters down hole. Gold assay values for individual core samples, each being 3.0 m in length, ranged from 0.32 to 3.33 g/t Au. No other gold pathfinder elements were enriched in this zone. Drill-hole 138-95-19 appears to have passed through a portion of the same mineralized zone intersected by hole 139-95-08 and produced an 8-meter-long interval, starting 48 m down-hole, that averaged 0.653 g/t Au. 

Central Target Area

A linear series of pits and small underground workings extend from the peak of Cerro Magallanes eastwards down slope and define the Central target area. The westernmost occurrence of gold mineralization as sampled by Riverside at an elevation of about 2,170m a.s.l.  Two adjacent 1.5 m long channel samples returned gold assays of 3.0 and 7.9 g/t Au, with another 2 m-long sample collected 5 m to the side assaying 9.0 g/t Au.  Samples were collected along a fault breccia containing crystalline quartz, presumably striking east-northeast with a moderate dip to the southeast.  It is possible that the intersection of this structure with the 35-40° easterly inclined slope surface of Cerro Magallanes has resulted in the linear array of gold showings, tested by historical workings and several Cambior drill-holes.  

At an elevation of about 1,930m a.s.l. are the underground workings of Obra-16 consisting of an adit and small galleries on three levels, 5-10 meters apart which collectively together have a length of 438 m. Thirteen Cambior samples on the upper level of this working assayed between 0.5 and 7.4 g/t Au, with another 16 samples from the deepest level assaying from 0.5 to 2.6 g/t Au. Riverside chip-sampled upslope from Obra-16. These 15 samples returned assays between 0.5 and 3.38 g/t Au.  Further upslope are the entrances to workings of Obra-19 and Obra-20.  Two boulders of coarse-grained, comb-textured quartz veining returned high-grade Au-Ag mineralization; samples 2466 and 2473 assayed 58.0 and 133.7 g/t Au, and 288.0 and 87.8 g/t Ag, respectively.  

The eastern end of the target area is marked by a 20 m by 12 m collapsed open-cut or ‘glory-hole’ that connects to the underground working of Obra-13. Cambior’s sampling here is documented as comprising fine, quartz-feldspar-porphyritic, rhyolite which hosts quartz-fluorite stringers, veinlets, and patchy breccia.  The 22 samples from this area assayed between 0.5 and 4.2 g/t Au. Riverside also collected 12 chip-channel samples from this area that ranged from 0.2 to 3.31 g/t Au and 13.1 to 145.6 g/t silver. Greater concentrations of silver are noted at this lower level which appears to be indicating a transition from gold only mineralization found at higher elevations into a gold-silver zone where lead and zinc are also somewhat enriched.

The eastern half of the Central target area between Obra-16 and the higher elevation workings of Obras-19 and 20 was tested by 5 drill-holes, 4 done by Cambior (138-09, -10, -13 and -17) and one drilled by CRM (DDH-83-4).  Results from the five drill-holes were generally weak, with the assays reported by CRM for hole DDH-83-04 considered to be unreliable.  Hole 139-95-17, drilled to the northwest at an angle of 45°, intersected a relatively broad zone of gold mineralization that started 30 m down-hole and continued to 72 m in the hole, averaging 0.49 g/t Au.  The maximum assay for this mineralized intercept was 3.26 g/t Au.

The eastern end of the target area, where the workings of Obra-13 and Obra-14 are found, was tested with another two Cambior drill-holes, 138-95-02 and 138-95-07, both of which returned no significant assays.

East Target Area

The East target area is represented by a north-easterly trending ridge at the lower eastern slope of Cerro Magallanes and is defined by clusters of anomalous gold.  At the southern end of the target area is the small underground working of Obra-10, while at the northern end, about 180 m NNE of Obra-10, are the workings of Obra-6 which occur at about 1,720m a.s.l., the lowest elevation of all the historical workings found at the project. Maximum gold assays for underground samples collected by CRM and Cambior were reported as 3.84 and 1.96 g/t Au, respectively. 

Fifteen Riverside chip-channel samples assayed between 0.199 and 2.36 g/t Au. An additional sample of ‘dump’ material collected at the entrance of Obra-6 assayed 8.42 g/t Au and 207 g/t Ag while another sample of quartz vein ‘float’ assayed 13.9 g/t Au.

The East target area was drill-tested by 3 drill holes; two drilled by Cambior and one by CRM.  Cambior’s hole 138-95-03 was drilled to the south-east directly beneath the working of Obra-10, while hole 138-95-06 was drilled from the other side of the ridge in a WNW direction stopping short of the inferred mineralized structure that was sampled on surface and in the old workings. Neither of the drill-holes intersected any appreciable gold. CRM drill-hole DDH-83-01 was collared about 70 m west of the Obra-6 working and was inclined to the south-east.  Core samples were collected intermittently down most of the length of hole, however the gold and silver values using the testing methods used is considered to be unreliable. 

The scientific and technical data contained in the summaries pertaining to the Cecilia Project was reviewed and approved by Ron Burk, P. Eng., a non-independent qualified person to Riverside Resources, who is responsible for ensuring that the geologic information provided is accurate and whom acts as a “qualified person” under National Instrument 43-101; Standards of Disclosure for Mineral Projects.