check the type of column using powershell within a splist

hi,

i have a column called BU in my splist in many site collections.i had created using with lookup datatype and  now  since my design is changed i  want to create this as  a a choice field with few default values. Can anyone please help how to check this using powershell? i mean check the  datatype of  column using PS and  if its lookup then need to delete the list and recreate it with choice field. i know hot to create a splist with choice field using PS, but  i am unable to get the code for existence of lookup or choice field.

$web = Get-SPWeb "http://sitename"

$fieldnamebu= "BU"

$mysplist =  $web.lists["mysplist1"]

$lookupfieldA="Lookup"

  foreach($sfield in $mysplist.fields)
  {
 # how to check the datatype pf column as lookup

  if ( ##todo####  -eq $lookupfieldA )
{
  $mysplist.Delete();
 $web.upate();
#
create the splist with  choice field
$spTemplate = $web.ListTemplates["Custom List"] 
#Create SPTemplate instance of Type Custom List
$web.Lists.Add("mysplist1", "for approvers", $spTemplate)   #Add list to site
$spList = $spWeb.Lists["mysplist1"]    #Get list instance
$spList.OnQuickLaunch = $True   
$spList.Update()    #Update list to reflect changes in site
$spFieldType = [Microsoft.SharePoint.SPFieldType]::Text      #Get Field type to create
$spList.Fields.Add("Mymn", $spFieldType, $false)      #Add new field to list
}
  }