The relationship between mineral composition, crystal structure and paragenetic sequence: the case of secondary Te mineralization at the Bird Nest drift, Otto Mountain, California, USA

Abstract

An unusually diverse array of 25 secondary Te oxysalt minerals has been documented from Otto Mountain, California, and 18 of these from the Bird Nest drift sublocality. A paragenetic sequence for these minerals is proposed, using observed overgrowth relationships plus spatial association data and data from other localities. Apart from Te and O, the components Pb, Cu and H are essential in the majority of the minerals. The atomic Cu/Te ratio decreases through the paragenetic sequence. This, and the occurrence of minerals with additional components such as Cl − , CO For the minerals with known crystal structures, two alternative 'structural units' were identified, one consisting only of the Te 4+ or Te 6+ oxyanion, while the other also included small, strongly-bound cations such as Cu 2+ . The degree of polymerization for the Te oxyanion correlated with the paragenetic sequence: the monomeric tellurate anions of early minerals were replaced progressively by dimers, chains and sheet structures, which may relate to a decreasing abundance of the 'network modifying' Cu 2+ cation, analogous to Bowen's discontinuous reaction series in igneous rock-forming silicates.No relationship was seen between paragenetic order and the larger type of structural unit, or structural complexity as defined by information content. This contrasts with results in the literature for evaporite sulfates and pegmatite phosphates. While structure-paragenesis relationships may be widespread, the exact nature of such relationships may be different for different chemical systems and different paragenetic environments.

Lead-tellurium oxysalts from Otto Mountain near Baker, California, USA: XII. Andychristyite, PbCu2+Te6+O5(H2O), a new mineral withhcpstair-step layers

“…Additional background on the occurrence is provided in Kampf et al (2010a), Housley et al (2011) and Christy et al (2016).…”

“…Andychristyite is a very rare phase, for which there are no observed contact relationships with other secondary minerals; however, considering the Te oxysalt paragenetic flowchart of Christy et al (2016), we can make some predictions about its place in the Otto Mountain secondary mineral paragenesis based on its chemistry and structure. The stoichiometries of andychristyite and eckhardite are identical, except that andychristyite contains Pb instead of Ca, and the crystal structures of both contain Te as [Te 2 O 10 ] 8-dimers.…”

“…Mills et al, 2012), and more recently for helping advance the knowledge of the crystal chemistry of tellurium (e.g. Mills and Christy, 2013;Christy and Mills, 2013;Christy et al, 2016). Andy Christy has agreed to the naming of this mineral in his honour.…”

A review of the structural architecture of tellurium oxycompounds

“…The recent explosion of new secondary mineral species, particularly from Otto Mountain, California, has seen publication of descriptions for 14 new Te minerals from 2010 up to September, 2015 (Kampf et al, 2010a;Back et al, 2011;Housley et al, 2011;Pekov et al, 2010;Christy et al, 2016). This represents the greatest flurry of activity in the study of Te secondary minerals since the 1970s.…”

Hagstromite, Pb8Cu2+(Te6+O6)2(CO3)Cl4, a new lead–tellurium oxysalt mineral from Otto Mountain, California, USA

“…Hagstromite is the 16th new mineral to be described from the remarkable Pb-Cu-Te-rich secondary mineral assemblage at Otto Mountain, near Baker, California, USA (Kampf et al, 2010a;Housley et al, 2011). A complete list of secondary Te oxysalts from Otto Mountain up-to-date through 2016 is provided by Christy et al (2016). Among the new Otto Mountain mineral species, only hagstromite and the recently described müllerite, Pb 2 Fe 3+ (Te 6+ O 6 )Cl (Mills et al, 2020), are not included in that list.…”