At A Glance | |
Ownership | 100% TVIRD owned |
Location | Alegria, Mainit, Tubod and Bacuag Municipalities, Surigao Del Norte Province |
Business activities | Mining and Processing of Gold and Silver ore. 100% of the dore produced is exported. |
Deposit Type | Replacement Type Deposit |
Resource | Combined Indicated and Inferred Underground Resource at 3.9M tonnes at 5.7 g/t Au and 7.7 g/t Ag |
Logistics | The site is situated 1km of private road from the national highway and is 35 km from Surigao City and 100 km from Butuan City, both with several daily flights from Manila and Cebu. There are also two (2) seaports in Surigao City and one (1) in Butuan City that can be used for marine cargoes. |
Production Phase | Project Stage |
The Siana Project which is located along Surigao Valley Fault is linked to other major gold mining centers in the country (Abra, Baguio, Masbate, Agusan and Davao) situated along the Philippine Fault Zone (PFZ), where deformation and mineralization are related to recurrent north-northwest trending segment of the PFZ.
The Siana deposit was initially mined by Suricon Consolidated Mining by underground method during the late 1930s until 1960. After a hiatus of 20 years, mining through open pit method was continued by Suricon from 1980 to 1991. Historical reports indicated roughly one million ounces of gold were produced by Suricon from Siana mine.
Greenstone Resource Corporation (GRC), a former Philippine subsidiary of an Australian-based company Red 5 Limited acquired the mining property in 2003. The Company invested in an extensive exploration drilling program to delineate the Siana mineralization along strike and its down-dip extension. A mining feasibility study was completed for Siana Project in 2009, allowing GRC to start construction in 2010.
More than US$200 million was spent by GRC to develop the Siana Project. A modern 1.1-million tons per annum Outotec mill, gravity and Carbon-in-Leach (CIL) mill facility was commissioned in 2012 at a capital cost of US$54 million that includes a single stage SAG mill and six CIL tanks. The mining facility built by GRC is ISO certified and has the only modern gold plant in the region which has the capacity to become a processing center for other nearby prospects. Also included in the assets of GRC is the Mapawa Project which is located north of Siana mine.
The Siana mining and processing activities were temporarily put on hold in April 2017 due to uncertainties in mining policy in the Philippines and challenges in obtaining environmental permits. During the period of suspension, site activities have been focused on dewatering the open pit, infrastructure maintenance and monitoring geotechnical issues.
In July 2021, TVI Resource Development (Phils.) Inc. completed the acquisition of the 100% outstanding shares of GRC and took over the operations of the Siana Gold Project and Mapawa Gold Project. GRC resumed project implementation under TVIRD in 2022 and completed its first dore shipment from plant commissioning in January 2023.
Based on the updated Mineral Reserve report by Mining One in July 2023, Siana Gold Project has an open pit reserve of 150,000 gold ounces and additional 570,000 gold ounces estimated for underground mining operations.
Located in Surigao Del Norte (Alegria, Mainit, Tubod and Bacuag Municipalities), Siana Project is covered by Mineral Production Sharing Agreement (MPSA) No. 184-2002-XIII which is composed of two non-contiguous northern and southern blocks, with total respective areas of 2,023.74 hectares and 1,265.03 hectares, respectively. Meanwhile, the Mapawa Prospect, which is located 20 kilometers north of Siana, is under MPSA No. 280-2009-XIII and covers 1,482 hectares.
The Siana Project site is approximately 30 aerial kilometers south of Surigao City and 84 kilometers north of Butuan City.
Surigao and Butuan are chartered cities that can be reached via daily flights from Manila, taking 1 hour and 10 minutes to Surigao and 1 hour 25 minutes to Butuan. Surigao, which has two (2) port facilities, can also be reached by sea from Manila
The Surigao Peninsula at the northeastern tip of Mindanao is characterized physiographically by a narrow north-northwest trending ridge, the Malimono ridge, and the wider and more geologically complex Diwata mountain range to the east. Intervening between these two topographic highs is a structurally-controlled valley, in fact a graben, from the Surigao lowlands in the north, to Lake Mainit and the Tubay Valley southwards. This topographically depressed corridor is interrupted by a young volcanic center, the Maniayao highlands, sitting north of Lake Mainit.
The oldest rock unit identified in Siana Project is the Bacuag formation, the limestone and marly sedimentary members of which mainly host the gold mineralization in the Siana mine. Unconformable on top of the Bacuag is the Middle-Late Miocene Mabuhay Clastics, observed southwest of the Siana pit, and the Late Miocene-Pliocene Timamana limestone, occurring as tower karsts mostly east of the Siana mine. The Bacuag and, probably, the Mabuhay clastics, are intruded by porphyritic andesite that is related to the Pliocene Maniayao volcanism. The andesite porphyry in the northern tip of the Siana pit is observed as post mineral intrusion to the Bacuag.
North-northwest trending faults are the major structures, several splays of which transect the parcel, including horse-tail splits in the north. Antithetic northeasterly faults are also observed to intersect the northwesterlies, as observed in the Siana pit.
Such geological setting continues in the southern portion of the Siana MPSA, including the Alegria claim, where regional north-northwest to south-southeast structures transecting Siana extend southwards. The dominant rock types in the Alegria parcel, however, are volcaniclastic sequences and the intruding andesite porphyry.
Siana is located along the Surigao Valley Fault, a major structure that is part of the Philippine Fault Zone. The area is known for various mineralization such as epithermal gold and porphyry-type copper-gold mineral deposits.
Mineralization in the Siana orebody occurs in both the limestone and basalt members of the Bacuag Formation, although earlier works describe mineralization to be confined only in the carbonates. Ore in the limestone occurs as either high grade sulphide-rich bodies consisting of pyrite, sphalerite, galena, chalcopyrite and quartz in cavities, or as disseminated gold in the clay or gouge portions and limestone.
Basalt-hosted mineralization to the east of the Siana pit occurs in soft, bleached, pyritic alteration zones, often 10 meters or more in width, over a lateral distance of approximately 140 meters. Minor mineralization also occurs within the volcaniclastics of the Mabuhay Formation. Mineralization progressively narrows to the south in both the carbonate and basalt hosts but is known to persist to approximately 400 meters below surface.
Reports indicate that the gold and sulphide mineralization present in the southern portion of the Siana tenement are hosted in andesite porphyry and intruded sediments where gold mineralization is more widespread. Exploration soil geochemistry indicates that a high level or near-surface epithermal system is possibly preserved in the area. A deeper copper-dominated type of mineralization reportedly appears to characterize the Alegria claim. Lenses of sulphide-rich bodies and hematite have been encountered in the immediate vicinity.
Similarly, the Mapawa prospect hosts a known gold and porphyry system with a number of several significant gold occurrences throughout the project area.
Early resource drilling on the Siana Project was conducted by Suricon Consolidated Mining Company (“Suricon”) from 1975 to 1981 through which 30 holes were drilled totaling 3,514 meters. A second campaign of drilling took place during the open-pit operations from 1983 to 1989, consisting of 47 holes with a total meterage of 6,893 meters. These holes were drilled from the open pit benches as the pit was progressively deepened.
GRC commenced its first drilling campaign in 2003. A limited program of Reverse Circulation (“RC”) and diamond drilling was undertaken with encouraging results. This was followed by a major diamond drilling program targeted along strike of, and below, the old open-pit. Drilling included specialized geotechnical and metallurgical holes.
The next phase of drilling was initiated in 2011, with holes drilled to the north, south and east of the Siana pit to follow up mineralization extensions along strike and at depth.
The database used for the Siana Mineral Resource Model includes 109 holes with 47,300 meters plus the 79 historic Suricon holes drilled between 1980 to 1990 for approximately 10,600 meters.
On the other hand, the Mapawa Mineral Resource Estimate was calculated based on a total of 78 diamond core drillholes with total meterage of 13,798 meters, comprising 5,628 meters of historical drilling completed by Suricon and 8,170 meters of additional drilling completed by GRC.
The latest mineral resource estimates for the Siana project have been detailed in the "Siana Feasibility Study Update and Ore Reserve Report," prepared by Mining One Consultants and dated June 11, 2023. These estimates, as declared by McKeown and Dumpleton in 2020, are pivotal in guiding the ongoing development and strategic planning for the mine's future operations.
| Classification | Cut-off Gold (g/t) | Tonnes (kt) | Gold (g/t) | Silver (g/t) | Cont. Gold (koz) | Cont.Silver (koz) |
| Probable | 2.4 | 3,010 | 4.1 | 6.7 | 396 | 644 |
| Total | 2.4 | 3,010 | 4.1 | 6.7 | 396 | 644 |
GRC had outlined a strategy to conduct approximately two years of open-pit mining, followed by a transition to underground mining which was expected to last for about eight years. Preliminary underground mine development has commenced effectively, with 445 meters of development completed and three portals established along with critical surface infrastructure for the operations. As at June 30, 2024, a total of 15.1 million tons of material have been moved of which 0.57 million tons were ore, aligning with the schedule to reach the main ore body by the first half of 2024. Implemented slope stability measures are in place to ensure safe and continuous mining operations.
The Process Plant at the Siana Mine was successfully commissioned ahead of schedule in December 2022. As part of the commissioning phase to temporal shutdown in August 2023, the mill processed 366,249 ore tons with average grade of 0.68 g/t gold and 4.37 g/t silver.
Upon resumption in March to end June 2024, the mill processed 201,938 ore tons of feed over 99 running days, with an average throughput of 2,040 tons per day. Efforts to test the maximum capacity of the plant led to a peak throughput of 3,000 tons per day during this period.
A strategic stockpile of medium and high-grade ore has been established for blending with lower grade ore to optimize feed to the Process Plant.
As of March 2023, Tailings Storage Facility (TSF 6) was commissioned and is actively containing tailings discharge from the Process Plant. Hydrotesting of the pipelines connecting the Process Plant to TSF-6 was successfully completed.
Preparation for the underground mine development is underway with a target start in Q1-2025.
