An arrestingly upsetting, though lyrically shot opening sets the tone, if not the pace, of “Vazante,” the solo feature directorial debut from Walter Salles collaborator Daniela Thomas (who co-directed “Foreign Land,” Midnight,” and the Cannes-awarded “Linha de Passe”). In fragmented and impressionistic close ups — a white hand grasping a sheet, a slave’s black face falling in and out of focus as she exhorts her mistress to push — Thomas begins her film with a scene of childbirth that is also a scene of death, and it is not the last time these two concepts will appear inextricably intertwined in her darkly mysterious period fable.

Mining life in Brazil in the early 1800s is, according to her envisioning, haughty and brutal, where man’s inability to wholly tame nature gives rise to the inarticulate rage of white landowning men who oppress women and slaves alike in a futile attempt to master their destinies. These are gruff and mighty themes, and with a tighter edit that would excise some of the more directionless detours, Thomas’ film could be as powerful as it is beautiful.

It is the wife of wealthy slaveowner Antonio (a gaunt, haunted Adriano Carvalho) who dies in the opening, along with her stillborn son. And so Antonio returns with a chest full of now useless baptismal robes for the infant and a retinue of slaves chained by the neck, to his enormous, isolated holding in the Brazilian countryside and is waited upon, along with his senile elderly mother, by tenants, locals and relatives wishing to pay their respects.

One such family, that of the dead woman’s brother, includes 12-year-old Beatriz (striking newcomer Luana Nastas), who catches Antonio’s eye and whom he duly marries. Frequently absent on business, while he waits for his child-bride to reach childbearing age, Antonio takes slave Feliciana (Jai Baptista) to his bed, while Beatriz experiences the first bloom of young love with Feliciana’s son, Virgilio (Vinicius Dos Anjos).

Meanwhile, subplots abound within the slave community, as a new group, who do not speak the same language as the others, refuses to submit, and a new freed-man overseer, Jeremias (Fabrício Boliveira), arrives. A black Brazilian native rather than an African, Jeremias has ideas about turning the land, on which the mines are no longer yielding many diamonds, into a plantation farm, and a brutal approach to discipline.

It’s in the those latter reeds that Thomas loses the strands of her narrative most frustratingly. The proud Lider (Toumani Kouyaté), the de facto leader of the rebel faction of slaves, almost effects an escape but elects to return to bondage, saving his master’s life instead, and while that seems like it’s going to form a major part of the story, he then largely disappears from the film, and we never learn the reason for his change of heart, nor why it evidently made so little difference to his status. Similarly the black-on-black violence enacted by Jeremias on the Africans under his charge is a potentially fruitful avenue on which Thomas’ screenplay, co-written with Beto Amaral, fails to fully capitalize.

Instead Thomas’s narrative gaze frequently defocuses, electing to evoke a mood of drowsy menace as Antonio or Beatriz wander, separately, through the forbidding landscape. But DP Inti Briones’ gorgeously textured photography, which captures candlelit interiors and elemental exteriors with sensuous attention to detail, is so strong that it can summon that moody atmosphere in single, beautifully composed frames — it doesn’t need to be dwelt on quite so heavily.

At its best, with its stunning black-and-white imagery, eloquent and precise sound design, and taciturn yet characterful performances, “Vazante” can recall the heady, inky expressiveness of recent art-house hit and Oscar nominee “Embrace of the Serpent.” But Thomas’ film is paradoxically more generic and less coherent than Ciro Guerra’s Amazonian odyssey, and it builds to a melodramatic finale that is almost gimmicky in its contrivance, however historically well-founded it may be.

These narrative missteps are a pity (though again, nothing that a more single-minded edit couldn’t fix) because when Thomas’ film does find its voice, it is as authentically immersive an experience of a harsh and loveless past as one could hope for, composed of the sensual details that can make the pleasures and horrors of 200 years ago feel like now: bare feet sinking into mud; rain on skin; children’s fingers, black and white, scooping porridge from a communal pot; or a young girl’s clear eyes, flickering under closed lids as her whole body stiffens at her husband’s approach.