Cecilia Gold-Silver Project

Best assays: 133.7 g/t Au and 335 g/t Ag.

Low Sulphidation Epithermal Au-Ag Rhyolite Flow Dome Complex.

Drill Permitted, Available for Option.

Location: Sonora, Mexico.

Commodities: Gold and Silver.

Size: 7,739.4 has


The Cecilia Project is a district-scale gold and silver low sulfidation epithermal system centered on multiple mineralized rhyolitic flow-dome complexes. Mineralization is related to structures of N30W and N70E with high grades assayed at the intersection of these structures. One of the workings at the Cerro Magallanes dome returned high grades up to 133.7 g/t Au and 335 g/t Ag. In addition to the rhyolite domes the underlying sedimentary Cabullona group and Paleozoic limestone provide an environment for replacement style mineralization at depth. Riverside’s current analogues for Cecelia are SSR Mining’s Pitarrilla deposit and Fresnillo’s San Julian deposit, which contain 526 million oz Ag (Measured + Indicated 1) and over 230 million oz Ag respectively.

The Cecilia Project is located 40 km southwest of the Mexico-U.S.A. border town of Agua Prieta in Sonora, Mexico. The project is directly accessible by well-maintained dirt road from highway 17.

1 https://www.ssrmining.com/_resources/Pitarrilla_Technical_Report_Dec_14_2012.pdf

Figure 1: Interpretative cross-section of Cerro Magallanes rhyolitic dome


As many as 30 abandoned exploration adits, small underground galleries and surface prospect pits are distributed over the upper slopes of Cerro Magallanes, which are believed to date back to the early decades of the 20th Century. 

In the early 1980s, the Consejo de Recursos Minerales (CRM) initiated a project at Cerro Magallanes over a 3-year period and carried out a comprehensive exploration program, including:

  • 896 km2 of regional mapping
  • 635 surface rock chip samples
  • 14.3-line kilometers of induced polarization
  • 1,412 m of underground mapping
  • 4 diamond drill holes totaling 732.3 m

In April of 1994, Cambior Exploracíon entered into an option-to-purchase agreement with the Mines General Directorate (DGM) for the project. Cambior terminated the contract at the end of the first 18-month term, their work 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-kilometers 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 totaling 3,817.6 m

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

In February of 2013, Precipitate Gold Corp. entered into an option agreement with Gunpoint Exploration Ltd., who then controlled the La Cecilia project. Precipitate Gold, collected 43 surface rock chip samples and resampled and analyzed 35 samples from 2 drill holes. 

In 2017, Riverside Resources undertook rock-chip sampling to confirm the existence of the more intensely mineralized gold occurrences found on the Cerro Magallanes flow dome. Riverside confirmed work done by previous explorers, leading to additional mapping and a large soil grid completed in 2018, totaling over 1,300 samples.

Through this work, Riverside Resources successfully discovered new mineralized areas targets including the: Cerro Magallanes, La Mesa, Casa de Piedra, Medias Rojas, Cruz I and II and Magallanecito another dome complex.

Recent addition of 1,801 ha to the Cecilia Project land package has expanded work possibilities and discovery of new targets to the east.


Riverside completed a 1st phase exploration program at the North Breccia and Central Zones in 2017 collecting 91 rock chip and grab samples. Thirty-three (33) of the 91 samples yielded gold assays greater than 0.5 g/t gold (Au) with five samples assaying greater than 3 g/t Au. 

The three-best sampled assays were (see press release dated June 6, 2017):

  • 133.7 g/t Au with 288 g/t silver (Ag)
  • 58 g/t Au with 207 g/t Ag
  • 8.42 g/t Au with 87.8 g/t Ag

Nineteen (19) of the 91 samples have silver contents greater than 100 g/t Ag, six of these samples yielding assays that were greater than 200 g/t Ag and the maximum silver assay was 310 g/t Ag.

In September of 2018, Riverside completed a regional soil sampling program. The soil survey covered approximately 30% of the 50 kmCecilia 1 concession (see Figure 2 below and press release dated March 5, 2018), and has expanded the targeting around the known central Cerro Magallanes area of the Cecilia Project. The Company continues to advance and refine the known central targets and is also placing equal priority on new property-wide target generation.

Figure 2: Geochemistry zoning from Riverside soil sampling results

In October 2018, Riverside reported on rock chip channel samples from the Cerro Magallanes area continuing to expand exploration to different regional areas at the Project (see press release dated October 2, 2018). Riverside’s rock sampling results from the main central rhyolitic dome complex verifies and expands upon historical sampling for gold within breccias and veins on Cerro Magallanes. Dome margins also show positive potential for near-surface gold targets. This channel sampling program included 305 samples returning assays ranging from <0.05 to 19.0 g/t Au. Sampling shows consistent gold from the top of Cerro Magallanes (2200m) at the San Jose Target downslope to the northeast to the Agua Prieta-North Breccia Target and through to the Central and East Target (1760m) areas.

Results across the Cecilia 1 concession shows significant upside, with high-grade samples at Medias Rojas up to 12.5 g/t and a 2-m channel sample assaying 2.3 g/t at La Mesa Target. Similar to Cerro Magallanes, mineralization follows primary northeast and northwest-trending structural lineaments for which the intersection serves as an excellent migration path for gold-bearing fluids.


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 consisting of interbedded siltstone, fine-grained sandstone and thin layers of intraformational, immature pebble conglomerate (middle Cretaceous Cabullona Group), providing a perfect setting for replacement style mineralization at depth. This sedimentary sequence also extends over the Cecilia 1 and 2 concessions, in contact with Paleozoic limestone and Precambrian granite uplifted through horst and graben formation.

Gold mineralization is concentrated along NW and NE regional structural lineaments. Riverside Resources identified four targets on the Cerro Magallanes dome and six others outside of the dome. All of them show extensive alteration and sub-continuous high grades. Surface geochemistry indicates that that the areas sampled are above the boiling zone suggesting gold-bearing mineralization could be intersected at shallow depth at these targets.

Figure 3: Geological map of Cecilia 1 and Cerro Magallanes


Cerro Magallanes Dome encompasses four sub-targets: San Jose, North Breccia, Central Target and East Target (Figure 4). Riverside’s extensive work program since 2017 has shown a vertical variation with a significant concentration of Ag at the base of the dome along the eastern slope to gold-only enriched at the top of Cerro Magallanes. Three specific elevations: 1,700 m, 1,900 m, and 2,100 m comprise most of the high-grade, which suggests multiple mineralizing events within specific structural settings, along dome margin and stratigraphy. This style of mineralization is very similar to the Pitarilla mine in Durango, where large volumes of mineralized rock can be found in addition to high-grade structural bounding margins. This hypothetic target at Cerro Magallanes would be at 300 to 500 meters depth from the top of the dome, evident by the presence of the Cabullona sediments outcropping at 1,650 m elevation on the eastern slope.

Figure 4: Geological map of Cerro Magallanes with historical and Riverside’s rock sampling

  • The San Jose target is located at the top of the dome along the primary structural zone bisecting the peak of Cerro Magallanes. There are over half a dozen of old workings here, some of them accessing multiple parallel fault zones carrying gold mineralization of 47 m @ 1.12 g/t Au, 8 m @ 0.91 g/t Au (Cambior, 1995). At the surface, Riverside’s assays returned 3.0 and 7.9 g/t Au for a 1.5 m long channel and up to 9 g/t Au rock chip sample. These veins show classic epithermal multigenerational opening and filling textures typical of feeder zones like those at the San Julian Mine in Chihuahua also of the same mid-Tertiary age. 
  • North Breccia target has an outline of 250 m by 100 m and is marked by multiple zones of hydrothermal brecciation in porphyritic, flow banded and flow breccia rhyolitic rocks with strong hematite-stained silica alteration. Locally, crystallization of quartz and fluorite in open-space, as well as veinlets, is visible, however, the area shows primarily extensive fractures along NW-SE trend with strong hematite and clay-rich gouge material. Since 2017, Riverside Resources collected over 75 rock-chip samples in this area. Twenty-six of these samples returned gold assays ranging from 0.41 to 7.46 g/t Au. CRM and Cambior both drill-tested this area and intersected a 30 m interval of 1.41 g/t starting 4.0 meters downhole (138-95-08). The same portion of mineralization was intersected in hole 139-95-19 and produced an 8-m-long interval that averaged 0.65 g/t Au.
  • Central target is located along the same northwestern trend as the North Breccia and returned one sample of 133 g/t Au and 335 g/t Ag in mine dump. There are numerous small underground workings reportedly dating back to the 1940s that extend as a linear feature from the peak of Cerro Magallanes down the slope (Figure 5). Riverside Resources collected 30 samples across the target, which returned between 0.5 and 133.7 g/t Au with values worth noting such as 58 g/t Au and 19 g/t Au with reported respective silver values of 288 g/t Ag and 335 g/t Ag (See press release dated June 6, 2017). The Central target was tested by 5 drill holes in 1995. Hole 139-95-17 intersected 42.0 m averaging 0.49 g/t Au with a maximum assay of 3.26 g/t Au. Hole 138-95-9 & -10 intersected 36 m at 0.2 g/t Au and 60 m at 0.2 g/t gold.

Figure 5: Collapsed underground workings of Obra 14 at Central target. View to E-SE.


Cecilia 1 concession encompasses a wide range of rocks, from Precambrian granite to Paleozoic limestone and Cretaceous Cabullona sedimentary group. This succession was strongly affected by major NE and NW structural corridors that created a horst and graben terrain and northwest-trending rhyolitic dikes. The six targets, Casa de Piedra, La Mesa, Medias Rojas, Cruz 1, Cruz 2 and Magallanecito are located along the NE and NW regional structures.  Soil sampling geochemistry suggests near-boiling zone targets with anomalous gold exceeding 1 g/t (Precipitate Minerals, 2016, unpublished).

  • Casa de Piedra and La Mesa target both show the same style of mineralization primarily along NE trending faults extending for at least 2 km across the project area. Alteration and veining are visible within the Cabullona group rocks and increases in the limestone unit noted as jasperoid along structures and near rhyolitic dikes (see Figure 6 below). Some of the best results are located at La Mesa target with 2.81 g/t Au along a 2 m channel sample; and 0.907 g/t Au and 0.497 g/t Au at Casa de Piedra1. This area is believed to host a deeper target closer to the boundary of the limestone and the quartzite.
Figure 6: Casa de Piedra geological map showing Riverside’s Terraspec analysis, rock samples and structural targets
  • Medias Rojas is located along a NE trending structural corridor along which a more or less continuous vein/breccia/stockwork zone can be traced for at least 250 m. The corridor is about 20 m wide and comprises 3 to 5 parallel quartz veins with hematization of rare pyrite, sphalerite, and galena. Riverside’s best samples returned 12.5 g/t Au in sandstone and 8.5 g/t Au in rhyolitic dike material. Nineteen of the rock chip samples returned over 0.3 g/t Au. The extent of the mineralization along strike has not been established, but recent work suggests that the vein system extends to the northwest onto the Cecilia 2 concession.

Figure 7: Examples of breccia and veining within the Medias Rojas structural corridor.

Cruz I and II are located to the north of the Cecilia 1 concession along and near a major northwest-trending corridor that extends for at least 4 km. Geochemistry from soil sampling shows anomalous Te, Au, Pb, Zn, and Cu, suggesting that Cruz I and II could be located within the base-metal horizon of an epithermal system. In the field, mineralization is associated with veins and stockwork and alteration zones up to 100 m wide with pervasive, widespread sericitic and silica alteration; sulphides are rare but noted in this area. At Cruz I, ten samples were collected with four samples returning 0.1 to 0.5 g/t Au (see press release dated November 15, 2018).

Magallanecito is an additional rhyolitic dome similar to Cerro Magallanes. Results from sampling highlights a high correlation between gold and silver making this target a priority for additional groundwork.

Gold and Silver


Low Sulphidatio Epithermal Au-Ag Rhyolite Flow Dome Complex

Type of Deposit

Fronteras, Sonora


7,739.4 Ha

Surface Area




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