ketth.1  RECENT    ZINC    MINING    IN    EAST    TENNESSEE.  211 
the  silicic  and  carbonic  acids  were  derived  from  the  atmospheric 
waters,  and  the  sulphur  combined  with  the  blende  passed  away  in 
other  forms.  Associated  with  the  blende  is  a  large  amount  of  second- 
ary calcite,  which  probably  represents  redeposition  of  the  original 
limestone  material. 
The  ore  is  found,  as  has  been  already  stated,  in  masses  of  brecciated 
limestone  and  dolomite.  This  is  the  case  in  all  deposits  which  have 
been  exploited,  and  is  probabljT  true  for  the  remainder  of  the  region, 
where  there  are  only  surface  indications  of  the  ore.  The  breccias  are 
I  extremely  angular,  and  the  fragments  vary  from  minute  grains  up  to 
blocks  a  foot  or  two  in  size,  most  of  them  being  but  a  few  inches. 
Only  here  and  there  does  there  appear  to  have  been  much  change  of 
the  large  fragments  by  solution.  Their  edges  are  sharp  and  clear  in 
most  cases,  and  the  calcite  and  blende  are  practically  limited  to  the 
angular  spaces  between  them.  All  parts  of  the  formation  are  brecci- 
ated, including  dolomite,  limestone,  chert,  and  a  few  thin  slaty  partings. 
The  limestone  appears  to  have  been  more  subject  to  the  brecciating 
action  than  the  other  beds.  In  a  number  of  cases  a  single  bed  of  lime- 
stone appeal's  to  be  more  brecciated  than  the  overling  and  underlying 
beds. 
The  ore  body  consists  of  the  entire  mass  of  brecciated  rock.  The 
portions  of  this  which  are  richest  in  blende  are  selected  by  hand  for 
crushing  and  washing.  Thus  considerable  material  is  handled  which 
is  too  lean  to  be  profitably  worked.  Small  pockets  and  bodies  of  ore 
are  very  rich,  and  contain  as  much  as  50  per  cent  of  their  volume  in 
blende;  the  other  extreme  consists  of  large  blocks  of  limestone  with 
scattered  streaks  and  crystals  of  blende.  Taking  the  ore  bodies  as  a 
whole,  there  seems  to  be  no  regularity  or  system  in  the  distribution 
of  the  richer  pockets.  Such  defined  shape  as  they  have  is  roughly 
lenticular,  and  they  do  not  partake  of  the  character  of  fissure  veins. 
According  to  analyses  by  the  Roseberry  Zinc  Company,  90  per  cent 
of  the  concentrates  is  zinc  sulphide,  the  impurities  being  nearly  all 
calcium  and  magnesium  carbonate. 
The  mixture  of  blende  and  calcite  which  occupies  the  spaces  between 
the  limestone  blocks  has  various  forms.  Usually  the  two  minerals  are 
intergrown  at  random.  In  many  cases  there  is  a  separation  of  the  two 
minerals  into  bands  on  opposite  sides  of  the  fissure  or  space  between 
two  limestone  blocks.  In  this  respect,  and  for  small  distances,  the 
deposits  have  the  appearance  of  fissure  veins.  These  do  not  run  at 
any  regular  or  single  angle  or  group  of  angles,  however,  but  follow 
irregular  cracks  and  breaks  between  the  limestone  fragments.  By  far 
the  larger  part  of  the  ore  is  the  irregular  mixture  which  practically 
honeycombs  the  rock,  and  its  chief  variations  are  in  the  proportions 
of  blende,  calcite,  and  limestone.  In  the  deposits  west  of  Mascot  and 
at  Jefferson  City  are  here  and  there  to  be  seen  bright-yellow  stains  of 
