Osisko Development Provides Exploration Update at Tintic Project

Press Release

Montreal, Québec, August 7, 2024 – Osisko Development Corp. (NYSE: ODV, TSXV: ODV) (“Osisko Development” or the “Company”) is pleased to provide an update on exploration activities at its 100%-owned Tintic Project (“Tintic” or the “Tintic Project”), located in the historic East Tintic Mining District in central Utah, U.S.A. This includes results of recently completed surface and underground diamond drilling targeting potential copper-gold-molybdenum porphyry centers, underground chip sampling at the Trixie test mine (“Trixie”), and ongoing target generation work.

Chris Lodder, President, stated, “Early results from our systematic exploration approach are yielding valuable information in assisting with vectoring toward potential mineralized porphyry sources and large undiscovered polymetallic carbonate replacement deposits. We are seeing encouraging porphyry style mineralization in drill holes that are providing us with better understanding of the geometry, ore controls and zoning of mineralization at East Tintic. With this knowledge, we are well positioned to continue to vector towards more copper-rich areas believed to be the source of known mineralization at Tintic. Utah was most recently ranked by the Fraser Institute as the top mining jurisdiction globally, and we are excited at the future prospect of building on our presence there.”

BIG HILL PORPHYRY TARGET DRILLING

• Drilling Results. Two surface diamond drill holes, BH-DD-24-001 and BH-DD-24-002, have been completed at the Big Hill target Area in early May 2024 (see Figure 2).
• The first drill hole was completed to a depth of 1,297 meters (“m”) (4,257 feet (“ft”)) when it transitioned out of the prospective alteration zone. The second drill hole was repositioned at a modified angle and completed to a depth of 1,623 m (5,324 ft).
• Both drill holes intersected porphyry systems defined by at least three late-mineral monzonite porphyritic intrusive phases and an intrusion breccia over a vertical depth of approximately 1,500 m (see Figure 3).
• Although anomalous copper and molybdenum mineralization was encountered, including low visible presence of chalcopyrite, tennantite, and molybdenite, this was primarily localized along structures, and hydrothermal breccias, and the transition from calcareous rocks into quartzites. No significant intercepts of copper, gold or molybdenum were observed. The porphyries encountered to date are considered to lack evidence for the major fluid paths required to be the source of mineralization in the Tintic District.
• Results to date have shown that the porphyries and intrusion breccia display potassic alteration with anhydrite and pyrite veinlets, which have undergone variable retrograde alteration to illite-chlorite and have been overprinted by pyrophyllite, dickite, and kaolinite along fault zones. This combination of intrusive rocks and alteration are clear evidence of the presence of a porphyry style mineralization at Big Hill. However, they are weakly mineralized, late inter-mineral phases that often post-date the better mineralized early-porphyry intrusive phases in well known porphyry deposits.
• Big Hill West Target. The results of the recent and historical drill holes suggest that the early and potentially better mineralized intrusive phase could be in an untested area immediately west and southwest of the area drilled at Big Hill (see Figure 3).
• Early porphyry intrusions, with more intense veinlets and alteration, are thought to be required to explain the metal inventory of the Tintic District.
• Drill core to date has shown that carbonate rocks in the intrusion breccia are marbleized and, in places, altered to retrograde skarn. Some discrete intervals comprise a finer-grained monzonite porphyry which is cut by porphyry-style quartz and magnetite veinlets, some containing pyrite and molybdenite with clear B-type affinity (see Figure 1). These inter-mineral intercepts, only approximated in Figure 3, are considered as blocks or screens ‘floating’ in the late-mineral phases, indicating that there are early and likely better mineralized inter-mineral intrusive phases to be found at Big Hill.

Figure 1: Core photos from Big Hill drill holes showing texture of intrusive rocks and associated alteration, veinlets, and breccia-clasts characteristic of porphyries.

• The potassically altered late-mineral porphyries are chilled against the quartz-veined porphyry intervals, defining them as inter-mineral in timing. These inter-mineral intercepts (approximated in Figure 3) are considered as blocks or screens ‘floating’ in the late-mineral phases. A similar quartz-veined porphyry is more abundant in the core from BPC-08-002 drilled by Anglo American at Big Hill (see Figure 2) in 2008. This drillhole also included appreciable thicknesses of the same intrusion breccia.

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