- journal_title：The Canadian Mineralogist
- Contributor：Mao Mao ; Yuanming Pan
- Publisher：Mineralogical Association of Canada
- Date：2012-
- Format：text/html
- Language：en
- Identifier：10.3749/canmin.50.1.31
- journal_abbrev：Can Mineral
- issn：0008-4476
- volume：50
- issue：1
- firstpage：31
- section：Articles
Hemimorphite, a zeolite-like mineral commonly present in supergene non-sulfide Zn deposits and Zn mine tailings, is known to contain elevated levels of As, Cd, Cu and Pb. Cation-exchange experiments of a natural hemimorphite (Mapimi, Durango, Mexico) with 0.1 M CaCl<sub>2sub> solution at 110 ºC show that As and Cu are retained, whereas Cd and Pb are readily exchanged. The retention of As is consistent with previous single-crystal electron paramagnetic resonance (EPR) results that showed its occurrence as the substitutional As<sup>5+sup> ion at the Si site. Single-crystal EPR spectra of hemimorphite from the M’Fouati Pb-Zn mine (Reneville, Congo), measured at 120 K and 295 K, show a Cu<sup>2+sup> center. The best-fit spin Hamiltonian parameters g, A(<sup>63sup>Cu), P (<sup>63sup>Cu) and A(<sup>1sup>H) of this center at 120 K demonstrate that Cu<sup>2+sup> resides at the tetrahedral Zn site, not in the channels as suggested by a previous powder EPR study. Cadmium and Pb in hemimorphite are probably present in the channels; this would account for their contrasting behavior from As and Cu during the cation-exchange experiments. However, single-crystal EPR spectra of ten samples of hemimorphite from various Pb-Zn deposits, including those taken after gamma-ray irradiation for doses up to 55 kGy, did not detect any paramagnetic Cd or Pb centers.