Vancouver — Ongoing drilling by
Results from Turquoise Hill indicate that the primary gold-copper porphyry mineralization surrounds a core of secondary copper-rich covellite and chalcocite mineralization that lies beneath a supergene-enriched chalcocite blanket near the surface.
“This discovery of a second area of primary gold and copper porphyry mineralization at the Central zone significantly enlarges the scale of the project,” says Ivanhoe’s executive vice-president, Douglas Kirwin. “Given the strength and extent of the induced-polarization (IP) survey that stretches all the way to the Far North Oyu target, there is excellent potential to expand this discovery.”
The previously identified covellite-chalcocite mineralization at Central Oyu is believed to represent a separate mineralizing event that overprinted and replaced the primary chalcopyrite mineralization. The covellite-chalcocite mineralization would seem to extend outward and at depth, into more primary gold-bearing chalcopyrite mineralization.
To date, the primary chalcopyrite mineralization in the Central Oyu zone has been intersected by 10 widely spaced holes in an area measuring 1 km by 800 metres. Ivanhoe speculates that as drilling moves north, the Central zone merges into the North Oyu geophysical target.
Highlights from drilling in the Central zone of primary mineralization include the following:
r Hole 187 cut 102 metres averaging 1.4 grams gold per tonne and 0.84% copper starting at 334 metres down-hole.
r Hole 196 encountered 156 metres grading 0.43 gram gold and 0.84% copper starting at 294 metres down-hole.
r Hole 202 cut 136 metres of 0.58 gram gold and 0.89% copper starting at 280 metres down-hole.
r Along the northern flank of the covellite-chalcocite zone, hole 226, collared 200 metres north of OTD211, cut 58 metres of chalcopyrite mineralization grading 0.42 gram gold and 1.9% copper starting at 264 metres down-hole. This was followed by an additional 58 metres of 1.32 grams gold and 1.02% copper starting at a down-hole depth of 532 metres.
The two mineralized intervals in hole 226 indicate that primary chalcopyrite mineralization extends to the northern flank and may continue beneath the covellite-chalcocite zone. The gold-bearing chalcopyrite zone remains open laterally as well as at depth. Currently, Ivanhoe is drilling stepout hole 243, about 200 metres north of hole 226, in order to test the downdip extent and grade of these targets.
The Central zone is defined by a 1-km-by-500-metre IP anomaly north of the Southwest and South zones. So far this year, 16 holes have been drilled in the Central zone in an attempt to delineate copper and gold resources below the chalcocite-rich mineralization that was partially delineated by reverse-circulation drilling in 2000.
In the centre of the gold-bearing chalcopyrite mineralization in the Central Oyu zone lies a tabular zone of secondary covellite and hypogene chalcocite copper mineralization. This mineralization is known to be 200 metres wide and 600 metres along strike, with a vertical extent of 300-400 metres.
Significant intercepts in this zone include the following:
r Hole 211 cut 262 metres grading 0.89% copper and 0.08 gram gold starting at 64 metres down-hole. Included was a 114-metre interval of 1.33% copper and 0.11 gram gold.
r Hole 216 intersected 268 metres of 0.7% copper and 0.07 gram gold starting at 142 metres down-hole.
r Hole 217 returned 124 metres of 1.2% copper and 0.07 gram gold starting at 160 metres down-hole.
To date, the company has completed 50,000 metres of core drilling at the project.
Drilling between the Central and Southwest zones has identified strong chalcopyrite, covellite and chalcocite mineralization along the footwall of a large, northeast-trending structure that extends northeast from the Southwest Discovery area.
Hole 219, drilled in this area, intersected 392 metres grading 0.77% copper and 0.04 gram gold starting at 208 metres down-hole, including 152 metres of 1.06% copper and 0.04 gram gold.
At last report the Southwest zone alone hosted 13.8 million oz. gold and 6.9 billion lbs. copper within an estimated inferred resource of 821 million tonnes grading 0.52 gram gold and 0.38% copper. The estimate is based on a cutoff grade of 0.3% copper-equivalent.
The Southwest zone hosts a higher-grade core of 120 million tonnes grading 1.55 grams gold and 0.70% copper. Four related zones — Central, North, South and Far Southwest — were not included in the estimate. Ivanhoe plans to release an updated estimate in the third quarter.
Meanwhile, at Ivanhoe’s Kharmagtai project, 120 km to the north, drilling has intersected 102 metres grading 2.09 grams gold per tonne and 1.05% copper starting at a down-hole depth of 40 metres. This included a 46-metre section grading 3.98 grams gold and 1.59% copper. As well, the hole intersected another zone of mineralization, starting at 166 metres down-hole, grading 1.49 grams gold and 0.94% copper. The company reports that this hole is 80 metres southeast of another, which returned 74 metres of 2.24 grams gold and 1.16% copper, including 12 metres of 4.41 grams gold and 1.62% copper.
The drilling confirms the discovery of a significant zone of high-grade, porphyry-hosted, gold-copper mineralization similar in style to the high-grade zones at Turquoise Hill, 120 km to the south.
Ivanhoe is currently drilling hole 4, which, at last report, had reached a depth of 145 metres and intersected altered monzodiorite and host sediments. Chalcopyrite was first encountered at a down-hole depth of 89.2 metres, and the hole has remained in mineralization to its current depth. Mineralization consists of quartz veining with visible chalcopyrite, pyrite and rare native copper with associated strong magnetite, secondary biotite and tourmaline alteration similar to that encountered in holes 2 and 3.
The mineralized zone at Kharmagtai is outlined by a minor magnetic feature that lies within a larger group of magnetic anomalies identified within a 3-by-2-km area. Each of these anomalies represents a target that has porphyry-style alteration (and, in many cases, a coincident IP anomaly).
In addition to the Kharmagtai target, Ivanhoe has defined three copper-gold porphyry targets: Stockwork Hill, Chun and Ovoot Hyar. The company also has identified a sediment-hosted gold target, dubbed OV3. Trench sampling at OV3 encountered visible gold hosted in altered sediments and jasperoid replacement mineralization. Visible gold has been observed within quartz stockwork mineralization at the Stockwork Hill and Chun prospects.
The company is in the midst of a rotary drill program at OV3. To date, eight shallow holes, averaging 100 metres in depth, have been completed. Drilling indicates widespread silicification in volcanoclastic sandstones and siltstones centered over a large IP anomaly.
Ivanhoe holds mineral rights to more than 51,600 sq. km in Mongolia, most of which is within the South Gobi porphyry belt. Other high-priority targets within the belt include Shuteen, Oyut Ulaan, Chandman Uul, Oyut Ovoo and Saran Uul. By the end of the summer, the company expects to have 18 drills spinning on its Mongolian properties.
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