Jj. Cocheme et al., CHARACTERIZATION AND POTENTIAL ECONOMIC INTEREST OF AUTHIGENIC ZEOLITES IN CONTINENTAL SEDIMENTS FROM NW MEXICO, Mineralium Deposita, 31(6), 1996, pp. 482-491
In NW Mexico, zeolite deposits of potential economic interest occur in
continental sediments related to mid-Tertiary basin and range tectoni
sm. In central Sonora, where the stratigraphic column is thicker (e.g.
in the Moctezuma Basin), two superposed sequences of sediments are di
stinguished on the basis of their lithology and stratigraphy. They are
known as the Baucarit Formation. The lower sequence, Miocene in age a
nd 300 to 400 m thick, is indurated and consists mainly of sandstones
and conglomerates. The upper one, of variable thickness, consists of c
lays. Zeolites occur in both sequences as alteration products of volca
nic glass in beds of white intercalated rhyolitic tuff. Previously kno
wn outcrops of zeolitites from Rio Batepito (erionite), Tetuachi and S
an Pedro Ures (heulandite group), Divisaderos (chabazite) and several
other newly discovered occurrences are described in this work in terms
of mineral association, physical properties (porosity, thermal behavi
our) and chemical characteristics (major and trace elements for indivi
dual crystals and bulk rock). Heulandite-group minerals are also prese
nt as cement (30% by volume) of the sandstones from the lower sequence
. Amygdales and veins from basaltic flows intercalated within the lowe
st sediments contain a large variety of zeolite species: chabazite, st
ilbite, phillipsite, mesolite, erionite, thomsonite, heulandite and an
alcime. Zeolites in the pyroclastic beds intercalated in the upper seq
uence represent the highest economic potential because they are essent
ially monomineralic and constitute up to 80% in volume of the whole ro
ck. Because of the inhomogeneous distribution of amygdales, zeolites i
n the basaltic flows have a low economic interest.