diff --git a/bin/picca_metal_dmat.py b/bin/picca_metal_dmat.py
index 19432ff09..e73382d86 100755
--- a/bin/picca_metal_dmat.py
+++ b/bin/picca_metal_dmat.py
@@ -17,6 +17,8 @@
 from picca import constants, cf, utils, io
 from picca.utils import userprint
 
+#store the default silicon metals modelled in the CF/XCF
+DEFAULT_SI_METALS = ['SiIII(1207)','SiII(1190)','SiII(1193)','SiII(1260)']
 
 def calc_metal_dmat(abs_igm1, abs_igm2, healpixs):
     """Computes the metal distortion matrix.
@@ -279,6 +281,12 @@ def main(cmdargs):
                         help='Rebin factor for deltas. If not None, deltas will '
                              'be rebinned by that factor')
 
+    parser.add_argument('--fast-metals',
+                    action='store_true',
+                    required=False,
+                    help='compute only the metal correlations used by Vega'
+                       'i.e. 4 LyaxSi matrices and CIVxCIV')
+
     args = parser.parse_args(cmdargs)
 
     if args.nproc is None:
@@ -416,6 +424,12 @@ def main(cmdargs):
         for index2, abs_igm2 in enumerate(abs_igm_2[index0:]):
             if index1 == 0 and index2 == 0:
                 continue
+
+            if args.fast_metals:
+                if not (abs_igm1 == "LYA" and abs_igm2 in DEFAULT_SI_METALS) \
+                and not (abs_igm1 == "CIV(eff)" and abs_igm1 == abs_igm2):
+                    continue
+
             cf.counter.value = 0
             calc_metal_dmat_wrapper = partial(calc_metal_dmat, abs_igm1,
                                               abs_igm2)