Naopa Mine, Molango Municipality, Hidalgo, Mexicoi

Regional Level Types
Naopa Mine	Mine
Molango Municipality	Municipality
Hidalgo	State
Mexico	Country

The Naopa Mining Unit is located in the middle of the Molango Manganese District and counts with proved manganese carbonate reserves to be exploited in an open-pit deposit, such as manganese oxide reserves.

The eastern margin of Mexico, where the Huayacocotla rift basin developed due to the clockwise turning of the Yucatan block during the opening of the Gulf of Mexico. The Mn carbonate ore zone occurs at the basal 1 to 10 m of the Chipoco Formation. The host rocks lack fossils, but stratigraphic correlation indicates Oxfordian to Kimmeridgian age. Paleodepth was estimated at 100 to 300 m from sporadic beds with benthic fossils. The Mn ore comprises rhodochrosite with minor kutnohorite and Mn calcite.
The Chipoco Formation can be subdivided into three main lithologies consisting of argillaceous, laminated mudstones, packstones, and wackestones. The base of the Chipoco Formation immediately overlying the Santiago-Chipoco contact consists of approximately 0.5 m of a pyrite-rich, manganese carbonate referred to as the “A Bed”. Pyrite is abundant and occurs as thin laminae or 2- to 3-cm-thick homogeneous beds and small scattered framboids. The main ore zone, above the “A Bed,” consists of dark, laminated, fine-grained limestones, with interbedded calcareous shales and calcarenites. An enormous part of the ore zone is composed mainly of brown micrite and rhodochrosite with a clotted, pelletal, or intraclastic texture with a characteristic wavy lamination. The typical fine lamination shows variation of pale and dark-colored parallel laminae with evident soft-sediment deformation. Pyrite is minor, except locally, and fossils are rare. The ore beds also contain chlorite, magnetite, hematite, and organic matter as gangue minerals.
The Mn carbonate ore formation of the Molango deposits is of the Sedex-type, where Mn is derived at distal hydrothermal sources from the opening Gulf of Mexico in the time of the Kimmeridgian stage of the Late Jurassic epoch. Dissolved Mn(II) was subsequently concentrated in the Huayacocotla basin by oxygen-poor water. The dissolved Mn(II) was precipitated as manganese oxides when conditions became oxygenated due to the inflow of oxygenated open sea waters from the Atlantic Ocean.

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References