The scandal that brought down the Canadian Bre-X mining company in the mid-nineties is the inspiration behind “Gold,” but to call Stephen Gaghan’s film a dramatization of the episode would be an exaggeration as great as any spouted by Matthew McConaughey’s over-the-top self-styled prospector in the movie. Though the script by Patrick Massett and John Zinman borrows the general outline and a few details from the historical record, it uses them to confect a story far closer to fiction than documentary. Buoyed by McConaughey’s unabashedly way-out performance, the result is sporadically amusing but inconsistent and, in the end, unsatisfying.

In this version, McConaughey plays one Kenny Wells, who inherits the Reno, Nevada mining company Washoe founded by his granddad and built up by his father (a single-scene cameo by Craig T. Nelson). An economic downturn in the 1980s practically destroys the operation; Kenny is reduced to calling prospective investors from the watering-hole where his long-suffering girlfriend Kay (Bryce Dallas Howard) tends bar.

When all his attempts to start up a new prospecting scheme locally come to naught, Kenny heads to Indonesia to offer a partnership to Mike Acosta (Edgar Ramirez), a geologist whose theory of a “Ring of Fire” along the Pacific Rim once appeared to be vindicated by a huge copper strike but has since had little success. Certain that Acosta’s belief in a massive gold deposit far inland along a river is correct, Wells promises to provide funding for an exploratory dig at a site Acosta indicates as especially promising, and after a long process—including a protracted bout with malaria for Wells—they strike what tests indicate is a rich deposit.

So rich, in fact, that sharks are soon circling—particularly the aptly-named New York investment banker Brian Woolf (Corey Stoll), who initially promises Kenny both wealth and independence but in the end tries to orchestrate the takeover of the operation by shady mogul Mark Hancock (Bruce Greenwood). Wells also manages to lose Kay as a result of his overly friendly conversations with one of Woolf’s associates (Rachael Hill). When Wells tries to remain independent, Hancock uses political pressure to take over the operation, but you can’t keep Kenny and Mike down for long: they outsmart their rivals by doing business with the black sheep of President Suharto’s family, Danny (Jirayu Tantrakul).

But just as Wells seems to have triumphed, a twist sends everything into the tailspin that marked the Bre-X scandal. A series of flash-forwards to an interview Kenny has with a young fellow named Jennings (Toby Kebbell) is intercut with staged scenes of the aftermath to complement the voiceover from Wells that’s dominated the storytelling until the final reel, which Gaghan closes with a shot that leaves the question of who did what and when deliberately ambiguous.

There’s some rambunctious fun to all the financial shenanigans, especially because McConaughey throws himself into his role with such gusto. Boasting a pot belly (which, to be sure, isn’t entirely consistent), a snaggletooth grin and a bad comb-over, and almost always wielding a cigarette, a drink or both, he cuts a larger-than-life figure as the brash redneck who never seems to settle down, except when he’s bedridden with malaria. By contrast, Ramirez is the cool, collected customer, impeccably dressed even in the jungle heat, who looks comfortable while Wells sweats profusely stripped down to his tighty-whiteys. They’re obviously intended to be the odd couple of the prospecting game, and the duo pull off the act decently enough, even if McConaughey is clearly the senior partner.

There are some colorful supporting turns, most notably by Stoll and Tantrakul, and Stacey Keach shows up briefly as a Reno banker. But Howard gets short shrift as Kay, though she looks terrific in a New York party scene. Cinematographer Robert Elswit brings a degree of visual energy to the images that matches the extreme extroversion of McConaughey’s performance, and the other technical technical contributions are pro down the line. The Indonesian sequences, shot in Thailand, certainly boast an authentic feel.

In the end, though, “Gold” works better as a pure star vehicle than as a tale of the dark side of the American Dream. McConaghey is fun to watch, but the narrative he dominates is less clever than its makers apparently hoped.