* Firm betting on big Namibia find
* Stock closed up 10.8 pct on Friday
SAO PAULO, May 10 (Reuters) - The chief executive and founder of Brazil's HRT Participações em Petróleo SA has resigned just as the firm begins drilling off Namibia's coast in the hope of making a major oil discovery, according to a securities filing on Friday.
Marcio Mello, a distinguished geologist and one of the architects behind the subsalt oil finds in Brazil's offshore Campos Basin, will remain on HRT's board of directors, the filing said. HRT spokesmen had no further comment his resignation.
In an April 22 interview with Reuters, Mello said he was baffled by investors' readiness to sell the company's shares, which had lost 90 percent since reaching an all-time high in 2011.
The stock closed up 10.8 percent on Friday.
Though he was banking on an area the company has said may hold about 10 billion barrels of oil, Mello told Reuters last month that existing natural gas discoveries in Brazil's Amazon would soon provide steady revenue.
HRT has the backing of international partners such as Russia's NK Rosneft AO and Portugal's Galp Energia SGPS SA. Rosneft committed to buying an additional 10 percent of HRT's Amazon unit next year, raising its stake to a majority 55 percent.
HRT was founded in the aftermath of the official end of state-run firm Petrobras' oil monopoly in 1997 and was once the largest oil service company in Brazil before it became an exploration company.
Mello is the former president of the Latin American section of the American Association of Petroleum Geologists and Latin America Section and President and founder of the Brazilian Association of Petroleum Geologists.
His replacement has not been announced.