Riverside Resources Intersects Near-Surface Gold and Base Metal Mineralization at Union Norte and Advances Multiple Targets for Phase 2B Drilling

VANCOUVER, British Columbia, Sept. 09, 2026 (GLOBE NEWSWIRE) -- Riverside Resources Inc. ("Riverside" or the "Company") (TSX-V: RRI) (OTCQB: RVSDF) (FSE: 5YY0), is pleased to report the assay results from the Phase 2A summer 2026 core drilling campaign following up on the high-grade gold-zinc mineralization and successful Phase 1 drilling of late last year. The Phase 2A drill program at the Union Project in northwest Sonora, Mexico has again intersected gold and base metals, continuing to expand upon the carbonate hosted replacement deposits (CRD) associated with past mining while also delivering success at new targets and advancing district-wide targeting. The exploration work is being carried out by Riverside in partnership with Questcorp Mining Inc. (CSE: QQQ), who is earning into the project through an option agreement (see news release, May 6, 2025). The success from this part of the program, which included core drilling, can now be expanded upon when Phase 2B drilling resumes following the seasonal break for the monsoon rainy season, which typically wraps up toward the end of September. These results confirm two main target areas. The program will continue drilling these areas, along with sediment-hosted gold targets at Luis Hill and vein targets at the Jabali area. Union and Union Norte drill results are summarized below, with further drilling planned for the Phase 2B drill campaign.

Phase 2A Highlights

An initial 7 holes were drilled with positive drill intercepts at the Union Mine and Union Norte areas (Figure 1) comprising Phase 2A which will then be next followed with Phase 2B after monsoon season ends in early October 2026.

• UND26-015 at the Union Norte target returned 14.60 m of 0.45 g/t Au Eq starting at 1.0 m with higher interval of 7.60 m grading 0.80 g/t Au Eq and 4.60 m of 1.09 g/t Au Eq from 8.00 m. This hole successfully crossed an interpreted NNW-trending feeder structure with anomalous gold, lead, and zinc values from near surface and can be next drilled along strike and down dip to continue to expand as shown in figure below.
• UND26-014 at the Union Norte target returned 9.10 m of 0.76 g/t Au Eq from 1.90 m, including a higher-grade subset of 1.5 m of 3.38 g/t Au Eq from 9.50 m confirming the near-surface mineralized feeder structure along strike from UND26-015 as can be seen in figure below.
• UND26-013 at the Union Mine intersected the continuity of the historic Sproul manto mine near the past underground mining, with anomalous Pb and Zn values indicating proximity to the replacement body which can be followed up with additional drilling.
• Induced Polarization survey at Luis Hill delineated a large chargeability anomaly extending over 1 km in strike along the IP line and with a 200 m depth thickness of a chargeable signal interpreted to potentially be associated with the sediment-hosted gold target identified in Phase 1 drilling (see news release, January 22, 2026). The anomaly remains ready for follow up drilling.

"Working with our partner Questcorp, we are pleased with the positive results from the initial part of Phase 2 drilling, and we look forward to further drilling once the rainy season ends. Grades above 0.5 g/t are significant, as mines in the region produce at this grade or higher. We see high grades in old workings, at surface, and in targets within the CRD-style and sediment-hosted bulk gold-style mineralization. Consistent near-surface intercepts are encouraging, with grades similar to those at nearby operations near Union. The positive results at the Union and Union Norte targets build on our last drill campaign, and we can now move to Phase 2B drilling at these areas, as well as additional locations outlined in the exploration program," said John-Mark Staude, CEO of Riverside Resources.

Figure 1. Drill Collar Location Map - 2025-2026 Drill Program. The figure illustrates the collar locations for both 2025 and 2026. The 7 drill holes reported in this news release are in green. Section lines correspond to drill cross-sections presented in Figures 2, 3, and 4. Collar coordinates are summarized in Table 2

Phase 2A Drill Results

Union Norte Target

The Union Norte Target is located 1.5 km north of Union Mine (Figure 1), where recent underground sampling returned 20.2 g/t Au and 226 g/t Ag with 2.7% Zn over a 30 m channel at the Union Mine (see news release, January 22, 2026).

UND26-014 and UND26-015 were designed to test the NNW-trending feeder structure identified through surface sampling, which returned values from 4.0 to 9.0 g/t Au with anomalous Pb and Zn. Both drill holes intercepted the structure at shallow depth, with UND26-015 returning 14.60 m of 0.45 g/t Au Eq from 1.0 m and UND26-014 returning 9.10 m of 0.76 g/t Au Eq from 1.90 m (Figure 2).

These results indicate the potential for a larger mineralized system, supported by the continuity of this structure and the host Clemente Formation as a major CRD host lithology, with potential for sediment hosted gold in the reactive shales above and below the CRD host carbonate. Some of the high angle, cross cutting feeder structures, or (“chimneys”), can be projected northward toward the La Negra target, where surface sampling and mineral evidence indicate hydrothermal activity that remains untested by drilling and could fit well within the upcoming drill program.

Figure 2: Drill Section (30 m thickness) through the Union Norte Target (looking northwest); section line A-A’ Figure 1.

Table 1: Assay results for UND26-014 and UND26-015 Union Norte

	From (m)	To (m)	Width (m)	Au_Eq (g/t)	Au_ppm	Ag_ppm	Cu_ppm	Pb %	Zn %
UND26-015	1.00	15.60	14.60	0.45	0.19	10.21	96.61	0.08	0.17
including	8.00	13.60	5.60	0.96	0.48	12.86	209.88	0.21	0.44
including	8.00	12.60	4.60	1.09	0.56	14.13	211.80	0.26	0.53
including	9.60	12.60	3.00	1.10	0.30	20.60	324.50	0.40	0.81
UND26-014	1.90	11.00	9.10	0.76	0.34	9.25	74.35	0.11	0.53
including	1.90	2.60	0.70	1.97	0.30	25.57	541.74	1.00	6.67
including	4.50	11.00	6.50	0.84	0.44	2.85	57.29	0.11	0.72
including	6.50	11.00	4.50	1.18	0.63	4.51	75.21	0.15	1.03
including	9.50	11.00	1.50	3.38	1.81	27.33	216.38	0.43	3.03

1. Reported intersections are calculated using a 0.10 g/t Au Eq cut-off grade. Maximum inclusion of 20 consecutive metres below cut-off grade.
2. True thickness of mineralization is unknown as the Company is still conducting exploration
3. AuEq Calculation Gold-equivalent values (AuEq) were calculated using USD metal prices of $1,700/oz gold, $23.61/oz silver, $0.94/lb lead, $1.32/lb zinc, and $3.78/lb copper; metal recoveries of 92.9% for gold, 95.0% for silver, 80.5% for lead, 86.9% for zinc and 71.3% for copper; and payability factors as described in Table 14.12 of the 2023 Cristina Technical Report. The formula incorporating these factors is: AuEq = Au + 0.014*Ag + 0.480*Zn + 0.351*Pb + 1.246*Cu. AuEq calculations are reported for illustrative purposes only.
4. A summary assay table is available on the Company’s website.

Union Mine Target

UND26-013 was collared to test the southward extension of the Sproul manto; a previously mined orebody. The drill hole was successful in finding Pb and Zn mineralization and intercepted the replacement body south of the known artisanal workings. Anomalous Pb (>36 ppm) and Zn (0.1-0.7%) values confirm proximity to the CRD replacement body (Figure 3). Deeper drilling is warranted to intersect the interpreted main feeder structure beneath the Union Mine, where the highest-grade results on the project were obtained (20.2 g/t Au, 226 g/t Ag, 2.7% Zn over 30 m; (see news release, January 22, 2026). Further drilling at the Union target can drill the newly identified IP features including the geologic targets that were progressed during the 2026 exploration work.

Figure 3: Drill Section (30 m thickness) through the Union Mine Target (looking north); section line B-B’ Figure 1.

Additional Phase 2A Targets

Jabali and Luis Hill Targets

Drill hole UND26-017, drilled southward toward the Jabali target, improved the understanding of the structural controls in this area. Elevated As values (10 – 80 ppm, Figure 4) indicate proximity to a feeder zone similar to those observed at Union Norte and the Union Mine and identified in the drill hole.

An IP survey at the project included lines at Jabali and Luis Hill with targets delineated as chargeability highs for both areas, particularly at Luis Hill, with the anomaly extending over 1 km along strike and 300 m at depth.  This IP feature at Luis Hill coincides with the sediment-hosted gold mineralization identified in Phase 1 drilling. The anomaly remains open along strike and at depth, significantly expanding the exploration footprint for this target Hole UND26-18 was drilled above the anomaly and terminated prior to reaching the 150 m planned target depth due to complications. Follow up drilling for Jabali and Luis Hill are warranted.

Figure 4: Drill Section (30 m thickness) through the Jabali Mine (looking northwest); section line C-C’ Figure 1.

Seven holes totaling 530.1 metres were completed during Phase 2A. Significant faulting within the targeted formations slowed core drilling and limited progress and recovery in several holes. To improve drilling efficiency in these ground conditions, the Company is actively evaluating a reverse-circulation contractor for Phase 2B. The change in drilling method is intended to increase penetration rates and improve access to priority targets while preserving the option to use diamond core where detailed geological information is required.

Table 2: Drill Collar Information for Drill Holes

Hole ID	East		North		Elev (m)		Azimuth (°)		Dip (°)		Depth (m)		Drilling Program
UND26-013	376137		3347087		364		55		-75		76.8		Union Mine
UND26-014	376169		3347610		400		30		-70		63.5		Union Norte
UND26-015	376169		3347610		400		320		-70		69.6		Union Norte
UND26-016	376112		3347670		388		160		-75		106		Union Norte
UND26-017	375593		3346327		367		190		-45		109.2		Jabalí
UND26-018	375188		3347547		410		0		-90		70		Luis Hill
UND26-019	375659		3347820		384		30		-70		35		El Cobre

Next Steps – Phase 2B

Drilling has been successful, with the first portion of the Phase 2 program meeting its objectives and delivering positive exploration results at both the Union mine and Union Norte targets. Restarting and continuing drilling at Union is warranted, with multiple targets identified, particularly those building on the recent drilling and geophysics completed at the property.

General Overview of La Union Project and Drill Coordinates

The Project is summarized in the published NI 43-101 Technical Report and, more briefly, on the Riverside website. Riverside initially acquired the Project and subsequently consolidated additional inlier mineral claims to build a strong land position. The company then advanced the Project through surface access agreements and drill permitting, making it a turnkey exploration opportunity for the Optionee.

At the Project, historical mining by Peñoles Mining Company targeted chimney and manto-style replacement bodies within the upper oxide zones. As a result, the underlying sulfide zones represent immediate drill targets for further exploration.

The Project features favorable limestone host rocks, an extensive alteration footprint, and multiple small-scale historical workings, with mineralization styles similar to those at the Hermosa Project in southern Arizona. At Hermosa, South32 is advancing mine development after acquiring the project from Arizona Mining for over $400 million, and Hermosa is now considered one of Arizona's most promising upcoming mining operations.

At La Union, immediate drill targets offer the potential for significant-scale discoveries. The Project is well positioned for near-term exploration results, with targets that include both oxide and deeper sulfide mineralization.

Qualified Person & QA/QC

The scientific and technical data contained in this news release pertaining to the Project was reviewed and approved by Julian Manco, P.Geo, a non-independent qualified person to Riverside Resources Inc., who is responsible for ensuring that the information provided in this news release is accurate and who acts as a "qualified person" under National Instrument 43-101 Standards of Disclosure for Mineral Projects.

All drill core samples were sawn in half, labeled, and bagged on site. The remaining half-core was retained and securely stored. Numbered security tags were applied to all sample shipments to ensure chain of custody. Samples were submitted to SGS's analytical facility in Hermosillo, Sonora, Mexico, for sample preparation and analysis. SGS is independent of the Company.

Analytical methods include fire assay for gold, gravimetric finish for high-grade silver, multi-element ICP digestion, and high-range fusion-ICP for over-limit concentrations.

The Company's QAQC program includes certified reference materials (CRMs), field blanks, and field duplicates inserted at regular intervals throughout each sample batch. CRM performance has had no failures yet identified and is evaluated using a Z-score criterion, where Z = (observed − certified value) / standard deviation, with acceptance thresholds of PASS (|Z| ≤ 2), WARNING (2 < |Z| ≤ 3), and FAIL (|Z| > 3). Field duplicate precision is assessed using relative percent difference (RPD), with PASS ≤ 20%, WARNING > 20–30%, and FAIL > 30%. Blanks are evaluated against the gold detection limit, with any result above that threshold flagged for investigation. Results below detection limits are retained as reported and excluded from RPD calculations. No QAQC failures have been found in the batches associated with the results reported herein.

About Riverside Resources Inc.

Riverside is a well-funded exploration company driven by value generation and discovery. The Company has a solid balance sheet with no debt and fewer than 95M shares outstanding with a strong portfolio of gold-silver and copper assets and royalties in North America. Riverside has extensive experience and knowledge operating in Mexico and Canada and leverages its large database to generate a portfolio of prospective mineral properties. Riverside has properties available for option, with information available on the Company’s website at www.rivres.com. 

ON BEHALF OF RIVERSIDE RESOURCES INC.

"John-Mark Staude"

Dr. John-Mark Staude, President & CEO

For additional information contact:

John-Mark Staude President, CEO Riverside Resources Inc. info@rivres.com Phone: (778) 327-6671 Fax: (778) 327-6675 Web: www.rivres.com	Eric Negraeff Corporate Communications Riverside Resources Inc. Eric@rivres.com Phone: (778) 327-6671 TF: (877) RIV-RES1 Web: www.rivres.com

Certain statements in this press release may be considered forward-looking information. These statements can be identified by the use of forward-looking terminology (e.g., "expect”,” estimates", "intends", "anticipates", "believes", "plans"). Such information involves known and unknown risks -- including the risk that the Transaction will not be completed as contemplates, or at all, availability of funds, the results of financing and exploration activities, the interpretation of exploration results and other geological data, or unanticipated costs and expenses and other risks identified by Riverside in its public securities filings that may cause actual events to differ materially from current expectations. Readers are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date of this press release.

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